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  • 201.
    Sainudiin, Raazesh
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Tillämpad matematik och statistik.
    Veber, Amandine
    Ecole Polytech, CNRS, CMAP, Palaiseau, France.
    Full likelihood inference from the site frequency spectrum based on the optimal tree resolution2018Inngår i: Theoretical Population Biology, ISSN 0040-5809, E-ISSN 1096-0325, Vol. 124, s. 1-15Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We develop a novel importance sampler to compute the full likelihood function of a demographic or structural scenario given the site frequency spectrum (SFS) at a locus free of intra-locus recombination. This sampler, instead of representing the hidden genealogy of a sample of individuals by a labelled binary tree, uses the minimal level of information about such a tree that is needed for the likelihood of the SFS and thus takes advantage of the huge reduction in the size of the state space that needs to be integrated. We assume that the population may have demographically changed and may be non-panmictically structured, as reflected by the branch lengths and the topology of the genealogical tree of the sample, respectively. We also assume that mutations conform to the infinitely-many-sites model. We achieve this by a controlled Markov process that generates 'particles' in the hidden space of SFS histories which are always compatible with the observed SFS. To produce the particles, we use Aldous' Beta-splitting model for a one parameter family of prior distributions over genealogical topologies or shapes (including that of the Kingman coalescent) and allow the branch lengths or epoch times to have a parametric family of priors specified by a model of demography (including exponential growth and bottleneck models). Assuming independence across unlinked loci, we can estimate the likelihood of a population scenario based on a large collection of independent SFS by an importance sampling scheme, using the (unconditional) distribution of the genealogies under this scenario when the latter is available. When it is not available, we instead compute the joint likelihood of the tree balance parameter beta assuming that the tree topology follows Aldous' Beta splitting model, and of the demographic scenario determining the distribution of the inter-coalescence times or epoch times in the genealogy of a sample, in order to at least distinguish different equivalence classes of population scenarios leading to different tree balances and epoch times. Simulation studies are conducted to demonstrate the capabilities of the approach with publicly available code.

  • 202.
    Sainudiin, Raazesh
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Tillämpad matematik och statistik.
    Yogeeswaran, Kumar
    Univ Canterbury, Dept Psychol, Christchurch, New Zealand.
    Nash, Kyle
    Univ Alberta, Dept Psychol, Edmonton, AB, Canada.
    Sahioun, Rania
    Univ Canterbury, Dept Psychol, Christchurch, New Zealand.
    Characterizing the Twitter network of prominent politicians and SPLC-defined hate groups in the 2016 US presidential election2019Inngår i: Social Network Analysis and Mining, ISSN 1869-5450, E-ISSN 1869-5469, Vol. 9, nr 1, artikkel-id 34Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We characterize the Twitter networks of the major presidential candidates, Donald J. Trump and Hillary R. Clinton, with various American hate groups defined by the US Southern Poverty Law Center (SPLC). We further examined the Twitter networks for Bernie Sanders, Ted Cruz, and Paul Ryan, for 9 weeks around the 2016 election (4 weeks prior to the election and 4 weeks post-election). We carefully account for the observed heterogeneity in the Twitter activity levels across individuals through the null hypothesis of apathetic retweeting that is formalized as a random network model based on the directed, multi-edged, self-looped, configuration model. Our data revealed via a generalized Fisher's exact test that there were significantly many Twitter accounts linked to SPLC-defined hate groups belonging to seven ideologies (Anti-Government, Anti-Immigrant, Anti-LGBT, Anti-Muslim, Alt-Right, White-Nationalist and Neo-Nazi) and also to @realDonaldTrump relative to the accounts of the other four politicians. The exact hypothesis test uses Apache Spark's distributed sort and join algorithms to produce independent samples in a fully scalable way from the null model. Additionally, by exploring the empirical Twitter network we found that significantly more individuals had the fewest retweet degrees of separation simultaneously from Trump and each one of these seven hateful ideologies relative to the other four politicians. We conduct this exploration via a geometric model of the observed retweet network, distributed vertex programs in Spark's GraphX library and a visual summary through neighbor-joined population retweet ideological trees. Remarkably, less than 5% of individuals had three or fewer retweet degrees of separation simultaneously from Trump and one of several hateful ideologies relative to the other four politicians. Taken together, these findings suggest that Trump may have indeed possessed unique appeal to individuals drawn to hateful ideologies; however, such individuals constituted a small fraction of the sampled population.

  • 203.
    Sainudiin, Raazesh
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Tillämpad matematik och statistik.
    Yogeeswaran, Kumar
    Univ Canterbury, Dept Psychol, Christchurch, New Zealand.
    Nash, Kyle
    Univ Alberta, Dept Psychol, Edmonton, AB, Canada.
    Sahioun, Rania
    Univ Canterbury, Dept Psychol, Christchurch, New Zealand.
    Rejecting the Null Hypothesis of Apathetic Retweeting of US Politicians and SPLC-defined Hate Groups in the 2016 US Presidential Election2018Inngår i: 2018 IEEE/ACM International Conference on Advances in Social Networks Analysis and Mining (ASONAM) / [ed] Brandes, U Reddy, C Tagarelli, A, IEEE, 2018, s. 250-253Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We characterize the Twitter networks of both major presidential candidates, Donald Trump and Hillary Clinton, with various American hate groups defined by the US Southern Poverty Law Center (SPLC). We further examined the Twitter networks for Bernie Sanders, Ted Cruz, and Paul Ryan, for 9 weeks around the 2016 election (4 weeks prior to the election and 4 weeks post-election). By carefully accounting for the observed heterogeneity in the Twitter activity levels across individuals under the null hypothesis of apathetic retweeting that is formalized as a random network model based on the directed, multi-edged, self-looped, configuration model, our data revealed via a generalized Fisher's exact test that there were significantly many Twitter accounts linked to SPLC-defined hate groups belonging to seven ideologies (Anti-Government, Anti-Immigrant, Anti-LGBT, Anti-Muslim, Alt-Right, Neo-Nazi, and White-Nationalist) and also to @realDonaldTrump relative to the accounts of the other four politicians. The exact hypothesis test uses Apache Spark's distributed sort and join algorithms to produce independent samples in a fully scalable way from the null model.

  • 204.
    Sakovich, Anna
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Tillämpad matematik och statistik.
    Sormani, Christina
    Lehman Coll, Dept Math, Bronx, NY USA.;CUNY, Grad Ctr, Bronx, NY USA..
    Almost rigidity of the positive mass theorem for asymptotically hyperbolic manifolds with spherical symmetry2017Inngår i: General Relativity and Gravitation, ISSN 0001-7701, E-ISSN 1572-9532, Vol. 49, nr 9, artikkel-id 125Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We use the notion of intrinsic flat distance to address the almost rigidity of the positive mass theorem for asymptotically hyperbolic manifolds. In particular, we prove that a sequence of spherically symmetric asymptotically hyperbolic manifolds satisfying the conditions of the positive mass theorem converges to hyperbolic space in the intrinsic flat sense, if the limit of the mass along the sequence is zero.

  • 205.
    Samuelsson, Robin
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Tillämpad matematik och statistik.
    Datorstödda bevis2014Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
  • 206.
    Samuelsson, Robin
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Tillämpad matematik och statistik.
    Multivariat databehandling och dataanalys: – en faktoranalys av slutbetyg i åk 9 inom Lgr11 på kommunnivå2016Independent thesis Advanced level (degree of Master (One Year)), 10 poäng / 15 hpOppgave
  • 207.
    Selin, Philip
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Tillämpad matematik och statistik.
    Auction Theory2016Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
  • 208.
    Shchekina, Anna
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Tillämpad matematik och statistik.
    Asian option pricing using graphics processing units2017Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
  • 209. Sircova, Anna
    et al.
    Karimi, Fariba
    Osin, Evgeny N.
    Lee, Sungmin
    Holme, Petter
    Strömbom, Daniel
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Tillämpad matematik och statistik.
    Simulating Irrational Human Behavior to Prevent Resource Depletion2015Inngår i: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 10, nr 3, artikkel-id e0117612Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In a situation with a limited common resource, cooperation between individuals sharing the resource is essential. However, people often act upon self-interest in irrational ways that threaten the long-term survival of the whole group. A lack of sustainable or environmentally responsible behavior is often observed. In this study, we examine how the maximization of benefits principle works in a wider social interactive context of personality preferences in order to gain a more realistic insight into the evolution of cooperation. We used time perspective (TP), a concept reflecting individual differences in orientation towards past, present, or future, and relevant for making sustainable choices. We developed a personality-driven agent-based model that explores the role of personality in the outcomes of social dilemmas and includes multiple facets of diversity: (1) The agents have different behavior strategies: individual differences derived by applying cluster analysis to survey data from 22 countries (N = 10,940) and resulting in 7 cross-cultural profiles of TP; (2) The non-uniform distribution of the types of agents across countries; (3) The diverse interactions between the agents; and (4) diverse responses to those interactions in a well-mixed population. As one of the results, we introduced an index of overall cooperation for each of the 22 countries, which was validated against cultural, economic, and sustainability indicators (HDI, dimensions of national culture, and Environment Performance Index). It was associated with higher human development, higher individualism, lower power distance, and better environmental performance. The findings illustrate how individual differences in TP can be simulated to predict the ways people in different countries solve the personal vs. common gain dilemma in the global limited-resource situation. This interdisciplinary approach to social simulation can be adopted to explain the possible causes of global environmental issues and to predict their possible outcomes.

  • 210.
    Sjödin, Elin
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Tillämpad matematik och statistik.
    Portfolio Performance Analysis2017Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
  • 211.
    Sjöholm, Sebastian
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Tillämpad matematik och statistik.
    Heteroscedasticity Models and their Forecasting Performance2015Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
  • 212.
    Sjöholm, Sebastian
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Tillämpad matematik och statistik.
    Past predicts the future with Supervised Learning and James-Stein theory2019Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
  • 213.
    Slegers, Wouter
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Tillämpad matematik och statistik.
    Spectral Theory for Perron-Frobenius operators2019Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
  • 214.
    Spaiser, Viktoria
    et al.
    Univ Leeds, Sch Polit & Int Studies, Leeds LS2 9JT, W Yorkshire, England.
    Hedström, Peter
    Linkoping Univ, Inst Analyt Sociol, Sociol, Norrkoping, Sweden;Linkoping Univ, Inst Analyt Sociol, Norrkoping, Sweden.
    Ranganathan, Shyam
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen.
    Jansson, Kim
    Linkoping Univ, Inst Analyt Sociol, Norrkoping, Sweden.
    Nordvik, Monica K.
    Linkoping Univ, Inst Analyt Sociol, Norrkoping, Sweden.
    Sumpter, David J. T.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Tillämpad matematik och statistik.
    Identifying Complex Dynamics in Social Systems: A New Methodological Approach Applied to Study School Segregation2018Inngår i: Sociological Methods & Research, ISSN 0049-1241, E-ISSN 1552-8294, Vol. 47, nr 2, s. 103-135Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    It is widely recognized that segregation processes are often the result of complex nonlinear dynamics. Empirical analyses of complex dynamics are however rare, because there is a lack of appropriate empirical modeling techniques that are capable of capturing complex patterns and nonlinearities. At the same time, we know that many social phenomena display nonlinearities. In this article, we introduce a new modeling tool in order to partly fill this void in the literature. Using data of all secondary schools in Stockholm county during the years 1990 to 2002, we demonstrate how the methodology can be applied to identify complex dynamic patterns like tipping points and multiple phase transitions with respect to segregation. We establish critical thresholds in schools' ethnic compositions, in general, and in relation to various factors such as school quality and parents' income, at which the schools are likely to tip and become increasingly segregated.

  • 215.
    Spaiser, Viktoria
    et al.
    University of Leeds.
    Ranganathan, Shyam
    Department of Statistics, Virginia Tech, Blacksburg, USA.
    Bali Swain, Ranjula
    School of Social Sciences, Södertörn University; Mistra Center for Sustainable Markets (MISUM), Stockholm School of Economics.
    Sumpter, David J. T.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Tillämpad matematik och statistik.
    The Sustainable Development Oxymoron: Quantifying and Modelling the Incompatibility of Sustainable Development Goals2017Inngår i: International Journal of Sustainable Development and World Ecology, ISSN 1350-4509, E-ISSN 1745-2627, Vol. 24, nr 6, s. 457-470Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In 2015, the UN adopted a new set of Sustainable Development Goals (SDGs) to eradicate poverty, establish socioeconomic inclusion and protect the environment. Critical voices such as the International Council for Science (ICSU), however, have expressed concerns about the potential incompatibility of the SDGs, specifically the incompatibility of socio-economic development and environmental sustainability. In this paper, we test, quantify and model the alleged inconsistency of SDGs. Our analyses show which SDGs are consistent and which are conflicting. We measure the extent of inconsistency and conclude that the SDG agenda will fail as a whole if we continue with business as usual. We further explore the nature of the inconsistencies using dynamical systems models, which reveal that the focus on economic growth and consumption as a means for development underlies the inconsistency. Our models also show that there are factors which can contribute to development (health programmes, government investment) on the one hand and ecological sustainability (renewable energy) on the other, without triggering the conflict between incompatible SDGs.

  • 216.
    Spaiser, Viktoria
    et al.
    Univ Leeds, Sch Polit & Int Studies, Social Sci Bldg, Leeds LS2 9JT, W Yorkshire, England..
    Sumpter, David J. T.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Tillämpad matematik och statistik.
    Revising the Human Development Sequence Theory Using an Agent-Based Approach and Data2016Inngår i: JASSS: Journal of Artificial Societies and Social Simulation, ISSN 1460-7425, E-ISSN 1460-7425, Vol. 19, nr 3, artikkel-id 1Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Agent-based models and computer simulations are promising tools for studying emergent macrophenomena. We apply an agent-based approach in combination with data analysis to investigate the human development sequence (HDS) theory developed by Ronald Inglehart and Christian Welzel. Although the HDS theory is supported by correlational evidence, the sequence of economic growth, democracy and emancipation stated by the theory is not entirely consistent with data. We use an agent-based model to make quantitative predictions about several different micro-level mechanisms. Comparison to data allows us to identify important inconsistencies between HDS and the data, and propose revised agent-based models that modify the theory. Our results indicate the importance of elites and economic inequality in explaining the data available on democratisation.

  • 217.
    Strömbom, Daniel
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Tillämpad matematik och statistik. Swansea Univ, Dept Biosci, Swansea, W Glam, Wales; Lafayette Coll, Dept Biol, Easton, PA 18042 USA.
    Dussutour, Audrey
    Université Paul Sabatier, Toulouse, France.
    Self-organized traffic via priority rules in leaf-cutting ants2018Inngår i: PloS Computational Biology, ISSN 1553-734X, E-ISSN 1553-7358, Vol. 14, nr 10, artikkel-id e1006523Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Ants, termites and humans often form well-organized and highly efficient trails between different locations. Yet the microscopic traffic rules responsible for this organization and efficiency are not fully understood. Recent experimental work with leaf-cutting ants (Atta colombica) on a very narrow trail has suggested a set of priority rules thought to govern the traffic dynamics. Here we implement an agent-based model to investigate the sufficiency of these rules with respect to producing the observed spatio-temporal properties of the traffic. We compare the model results to four statistics of the real ant flow and find that they share several key characteristics. Then we extend the model to a wider trail and compare the simulation results with new experimental data from this setting. We find that the extended model is able to reproduce the general features of the flow seen in the experiments, including the formation of three-lane traffic. The experimental finding that Atta colombica indeed organize the flow into three-lane traffic is important in its own right and contradicts the previously held belief that Atta in general do not. Due to the simplicity of the proposed rules we believe that they may be responsible for organizing the traffic flow on trails in other species of ant, and perhaps even other trail forming animals such as termites and humans.

  • 218.
    Strömbom, Daniel
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Tillämpad matematik och statistik. Lafayette Coll, Dept Biol, Easton, PA 18042 USA;Swansea Univ, Coll Sci, Dept Biosci, Swansea SA2 6PP, W Glam, Wales.
    Hassan, Tasnia
    Lafayette Coll, Dept Biol, Easton, PA 18042 USA.
    Greis, W. Hunter
    Lafayette Coll, Dept Biol, Easton, PA 18042 USA.
    Antia, Alice
    Carleton Coll, Dept Math & Stat, Northfield, MN 55057 USA.
    Asynchrony induces polarization in attraction-based models of collective motion2019Inngår i: Royal Society Open Science, E-ISSN 2054-5703, Vol. 6, nr 4, artikkel-id 190381Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Animal groups frequently move in a highly organized manner, as represented by flocks of birds and schools of fish. Despite being an everyday occurrence, we do not fully understand how this works. In particular, what social interactions between animals give rise to the flock structures we observe? This question is often investigated using self-propelled particle models where particles represent the individual animals. These models differ in the social interactions used, individual particle properties, and various technical assumptions. One particular technical assumption relates to whether all particles update their headings and positions at exactly the same time (synchronous update) or not (asynchronous update). Here, we investigate the causal effects of this assumption in an attraction-only model and find that it has a dramatic impact. Polarized groups do not form when synchronous update is used, but are produced with asynchronous update, and this phenomenon is robust with respect to variation in particle displacements and inclusion of noise. Given that many important models have been implemented with synchronous update only, we speculate that our understanding of the social interactions on which they are based may be incomplete. Perhaps previously unobserved phenomena will emerge if other potentially more realistic update schemes are used.

  • 219.
    Strömbom, Daniel
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Tillämpad matematik och statistik. Swansea Univ, Dept Biosci, Swansea, W Glam, Wales.
    King, Andrew J.
    Swansea Univ, Dept Biosci, Swansea, W Glam, Wales.
    Robot Collection and Transport of Objects: A Biomimetic Process2018Inngår i: Frontiers in Robotics and AI, E-ISSN 2296-9144, Vol. 5, artikkel-id 48Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Animals as diverse as ants and humans are faced with the tasks of collecting, transporting or herding objects. Sheepdogs do this daily when they collect, herd, and maneuver flocks of sheep. Here, we adapt a shepherding algorithm inspired by sheepdogs to collect and transport objects using a robot. Our approach produces an effective robot collection process that autonomously adapts to changing environmental conditions and is robust to noise from various sources. We suggest that this biomimetic process could be implemented into suitable robots to perform collection and transport tasks that might include - for example - cleaning up objects in the environment, keeping animals away from sensitive areas or collecting and herding animals to a specific location. Furthermore, the feedback controlled interactions between the robot and objects which we study can be used to interrogate and understand the local and global interactions of real animal groups, thus offering a novel methodology of value to researchers studying collective animal behavior.

  • 220.
    Sumpter, David J. T.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Tillämpad matematik och statistik.
    Szorkovszky, Alex
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Tillämpad matematik och statistik.
    Kotrschal, Alexander
    Stockholm Univ, Zool Dept, Stockholm, Sweden.
    Kolm, Niclas
    Stockholm Univ, Zool Dept, Stockholm, Sweden.
    Herbert-Read, James E.
    Stockholm Univ, Zool Dept, Stockholm, Sweden.
    Using activity and sociability to characterize collective motion2018Inngår i: Philosophical Transactions of the Royal Society of London. Biological Sciences, ISSN 0962-8436, E-ISSN 1471-2970, Vol. 373, nr 1746, artikkel-id 20170015Artikkel, forskningsoversikt (Fagfellevurdert)
    Abstract [en]

    A wide range of measurements can be made on the collective motion of groups, and the movement of individuals within them. These include, but are not limited to: group size, polarization, speed, turning speed, speed or directional correlations, and distances to near neighbours. From an ecological and evolutionary perspective, we would like to know which of these measurements capture biologically meaningful aspects of an animal's behaviour and contribute to its survival chances. Previous simulation studies have emphasized two main factors shaping individuals' behaviour in groups; attraction and alignment. Alignment responses appear to be important in transferring information between group members and providing synergistic benefits to group members. Likewise, attraction to conspecifics is thought to provide benefits through, for example, selfish herding. Here, we use a factor analysis on a wide range of simple measurements to identify two main axes of collective motion in guppies (Poecilia reticulata): (i) sociability, which corresponds to attraction (and to a lesser degree alignment) to neighbours, and (ii) activity, which combines alignment with directed movement. We show that for guppies, predation in a natural environment produces higher degrees of sociability and (in females) lower degrees of activity, while female guppies sorted for higher degrees of collective alignment have higher degrees of both sociability and activity. We suggest that the activity and sociability axes provide a useful framework for measuring the behaviour of animals in groups, allowing the comparison of individual and collective behaviours within and between species.

  • 221.
    Sverdlov, Oleksandr
    et al.
    Early Development Biostatistics, Novartis Institutes for Biomedical Research .
    Ryeznik, Yevgen
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Tillämpad matematik och statistik. Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Farmaceutiska fakulteten, Institutionen för farmaceutisk biovetenskap.
    Implementing Unequal Randomization in Clinical Trials with Heterogeneous Treatment Costs2019Inngår i: Statistics in Medicine, ISSN 0277-6715, E-ISSN 1097-0258, Vol. 38, nr 16, s. 2905-2927Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Equal randomization has been a popular choice in clinical trial practice. However, in trials with heterogeneous variances and/or variable treatment costs, as well as in the settings where maximization of every trial participant’s benefit is an important design consideration, optimal allocation proportions may be unequal across study treatment arms. In this paper, we investigate optimal allocation designs minimizing study cost under statistical efficiency constraints for parallel group clinical trials comparing several investigational treatments against the control. We show theoretically that equal allocation designs may be suboptimal, and unequal allocation designs can provide higher statistical power for the same budget, or result in a smaller cost for the same level of power. We also show how the optimal allocation can be implemented in practice by means of restricted randomization procedures, and how to perform statistical inference following these procedures, using invoked population-based or randomization-based approaches. Our results provide further support to some previous findings in the literature that unequal randomization designs can be cost-efficient and can be successfully implemented in practice. We conclude that the choice of the target allocation, the randomization procedure and the statistical methodology for data analysis are essential components to ensure valid, powerful, and robust clinical trial results.

  • 222. Sverdlov, Oleksandr
    et al.
    Ryeznik, Yevgen
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Tillämpad matematik och statistik.
    Wu, Sheng
    Exact Bayesian Inference Comparing Binomial Proportions, With Application to Proof-of-Concept Clinical Trials2015Inngår i: THERAPEUTIC INNOVATION & REGULATORY SCIENCE, ISSN 2168-4790, Vol. 49, nr 1, s. 163-174Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The authors revisit the problem of exact Bayesian inference comparing two independent binomial proportions. Numerical integration in R is used to compute exact posterior distribution functions, probability densities, and quantiles of the risk difference, relative risk, and odds ratio. An application of the methodology is given in the context of randomized comparative proof-of-concept clinical trials that are driven by evaluation of quantitative criteria combining statistical significance and clinical relevance. A two-stage adaptive design based on predictive probability of success is proposed and its operating characteristics are studied via Monte Carlo simulation. The authors conclude that exact Bayesian methods provide an elegant and efficient way to facilitate design and analysis of proof-of-concept studies.

  • 223.
    Szorkovszky, Alex
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Tillämpad matematik och statistik. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi.
    Kotrschal, Alexander
    Stockholm Univ, Zool Dept, Stockholm, Sweden.
    Herbert Read, James E.
    Stockholm Univ, Zool Dept, Stockholm, Sweden.
    Sumpter, David J. T.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Tillämpad matematik och statistik.
    Kolm, Niclas
    Stockholm Univ, Zool Dept, Stockholm, Sweden.
    Pelckmans, Kristiaan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Avdelningen för systemteknik. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Reglerteknik.
    An efficient method for sorting and quantifying individual social traits based on group-level behaviour2017Inngår i: Methods in Ecology and Evolution, ISSN 2041-210X, E-ISSN 2041-210X, Vol. 8, nr 12, s. 1735-1744Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    1. In social contexts, animal behaviour is often studied in terms of group-level characteristics. One clear example of this is the collective motion of animals in decentralized structures, such as bird flocks and fish schools. A major goal of research is to identify how group-level behaviours are shaped by the traits of individuals within them. Few methods exist to make these connections. Individual assessment is often limited, forcing alternatives such as fitting agent-based models to experimental data.

    2. We provide a systematic experimental method for sorting animals according to socially relevant traits, without assaying them or even tagging them individually. Instead, they are repeatedly subjected to behavioural assays in groups, between which the group memberships are rearranged, in order to test the effect of many different combinations of individuals on a group-level property or feature. We analyse this method using a general model for the group feature, and simulate a variety of specific cases to track how individuals are sorted in each case.

    3. We find that in the case where the members of a group contribute equally to the group feature, the sorting procedure increases the between-group behavioural variation well above what is expected for groups randomly sampled from a population. For a wide class of group feature models, the individual phenotypes are efficiently sorted across the groups and thus become available for further analysis on how individual properties affect group behaviour. We also show that the experimental data can be used to estimate the individual-level repeatability of the underlying traits.

    4. Our method allows experimenters to find repeatable variation in social behaviours that cannot be assessed in solitary individuals. Furthermore, experiments in animal behaviour often focus on comparisons between groups randomly sampled from a population. Increasing the behavioural variation between groups increases statistical power for testing whether a group feature is related to other properties of groups or to their phenotypic composition. Sorting according to socially relevant traits is also beneficial in artificial selection experiments, and for testing correlations with other traits. Overall, the method provides a useful tool to study how individual properties influence social behaviour.

  • 224.
    Szorkovszky, Alex
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Tillämpad matematik och statistik.
    Kotrschal, Alexander
    Stockholm Univ, Zool Dept, Stockholm, Sweden.
    Herbert-Read, James E.
    Univ Bristol, Sch Biol Sci, Bristol, Avon, England;Stockholm Univ, Zool Dept, Stockholm, Sweden.
    Buechel, Severine D.
    Stockholm Univ, Zool Dept, Stockholm, Sweden.
    Romensky, Maxym
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Tillämpad matematik och statistik.
    Rosén, Emil
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Tillämpad matematik och statistik.
    van der Bijl, Wouter
    Stockholm Univ, Zool Dept, Stockholm, Sweden.
    Pelckmans, Kristiaan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Reglerteknik.
    Kolm, Niclas
    Stockholm Univ, Zool Dept, Stockholm, Sweden.
    Sumpter, David J. T.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Tillämpad matematik och statistik.
    Assortative interactions revealed by sorting of animal groups2018Inngår i: Animal Behaviour, ISSN 0003-3472, E-ISSN 1095-8282, Vol. 142, s. 165-179Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Animals living in groups can show substantial variation in social traits and this affects their social organization. However, as the specific mechanisms driving this organization are difficult to identify in already organized groups typically found in the wild, the contribution of interindividual variation to group level behaviour remains enigmatic. Here, we present results of an experiment to create and compare groups that vary in social organization, and study how individual behaviour varies between these groups. We iteratively sorted individuals between groups of guppies, Poecilia reticulata, by ranking the groups according to their directional alignment and then mixing similar groups. Over the rounds of sorting the consistency of the group rankings increased, producing groups that varied significantly in key social behaviours such as collective activity and group cohesion. The repeatability of the underlying individual behaviour was then estimated by comparing the experimental data to simulations. At the level of basic locomotion, individuals in more coordinated groups displayed stronger interactions with the centre of the group, and weaker interactions with their nearest neighbours. We propose that this provides the basis for a passive phenotypic assortment mechanism that may explain the structures of social networks in the wild.

  • 225.
    Thulin, Måns
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Tillämpad matematik och statistik.
    A high-dimensional two-sample test for the mean using random subspaces2014Inngår i: Computational Statistics & Data Analysis, ISSN 0167-9473, E-ISSN 1872-7352, Vol. 74, s. 26-38Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A common problem in genetics is that of testing whether a set of highly dependent gene expressions differ between two populations, typically in a high-dimensional setting where the data dimension is larger than the sample size. Most high-dimensional tests for the equality of two mean vectors rely on naive diagonal or trace estimators of the covariance matrix, ignoring dependences between variables. A test using random subspaces is proposed, which offers higher power when the variables are dependent and is invariant under linear transformations of the marginal distributions. The p-values for the test are obtained using permutations. The test does not rely on assumptions about normality or the structure of the covariance matrix. It is shown by simulation that the new test has higher power than competing tests in realistic settings motivated by microarray gene expression data. Computational aspects of high-dimensional permutation tests are also discussed and an efficient R implementation of the proposed test is provided.

  • 226.
    Thulin, Måns
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Tillämpad matematik och statistik.
    On Confidence Intervals and Two-Sided Hypothesis Testing2014Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    This thesis consists of a summary and six papers, dealing with confidence intervals and two-sided tests of point-null hypotheses.

    In Paper I, we study Bayesian point-null hypothesis tests based on credible sets. A decision-theoretic justification for tests based on central credible intervals is presented.

    Paper II is concerned with a new two-sample test for the difference of mean vectors, in the high-dimensional setting where the number of variables is greater than the sample size. A simulation study indicates that the proposed test yields higher power when the variables are correlated. Computational aspects of the test are discussed.

    In Paper III, we discuss randomized confidence intervals for a binomial proportion. How some classical intervals fare is compared to how a recently proposed interval fares, in terms of coverage, length and sensitivity to the randomization.

    In Paper IV, a level-adjustment of the Clopper-Pearson interval for a binomial proportion is proposed. The adjusted interval is shown to have good coverage properties and short expected length.

    In Paper V we study the cost of using the exact Clopper-Pearson interval rather than shorter approximate intervals, in terms of the increase in expected length and the increase in sample size required to obtain a given length. Comparisons are made using asymptotic expansions.

    Paper VI deals with exact confidence intervals and point-null hypothesis tests for parameters of a class of discrete distributions. A large class of intervals are shown to lack strict nestedness and to have bounds that are not strictly monotone and typically also discontinuous. The p-values of the corresponding hypothesis test are shown to lack desirable continuity properties, and to typically also lack certain monotonicity properties.

    Delarbeid
    1. Decision-theoretic justifications for Bayesian hypothesis testing using credible sets
    Åpne denne publikasjonen i ny fane eller vindu >>Decision-theoretic justifications for Bayesian hypothesis testing using credible sets
    2014 (engelsk)Inngår i: Journal of Statistical Planning and Inference, ISSN 0378-3758, E-ISSN 1873-1171, Vol. 146, s. 133-138Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    In Bayesian statistics the precise point-null hypothesis theta=theta(0) can be tested by checking whether theta(0) is contained in a credible set. This permits testing of theta=theta(0) without having to put prior probabilities on the hypotheses. While such inversions of credible sets have a long history in Bayesian inference, they have been criticized for lacking decision-theoretic justification. We argue that these tests have many advantages over the standard Bayesian tests that use point-mass probabilities on the null hypothesis. We present a decision-theoretic justification for the inversion of central credible intervals, and in special case HPD sets, by studying a three-decision problem with directional conclusions. Interpreting the loss function used in the justification, we discuss when tests based on credible sets are applicable. We then give some justifications for using credible sets when testing composite hypotheses, showing that tests based on credible sets coincide with standard tests in this setting. 

    Emneord
    Bayesian inference, Credible set, Decision theory, Directional conclusion, Hypothesis testing, Three-decision problem
    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-216025 (URN)10.1016/j.jspi.2013.09.014 (DOI)000328593200012 ()
    Tilgjengelig fra: 2014-01-20 Laget: 2014-01-17 Sist oppdatert: 2017-12-06bibliografisk kontrollert
    2. A high-dimensional two-sample test for the mean using random subspaces
    Åpne denne publikasjonen i ny fane eller vindu >>A high-dimensional two-sample test for the mean using random subspaces
    2014 (engelsk)Inngår i: Computational Statistics & Data Analysis, ISSN 0167-9473, E-ISSN 1872-7352, Vol. 74, s. 26-38Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    A common problem in genetics is that of testing whether a set of highly dependent gene expressions differ between two populations, typically in a high-dimensional setting where the data dimension is larger than the sample size. Most high-dimensional tests for the equality of two mean vectors rely on naive diagonal or trace estimators of the covariance matrix, ignoring dependences between variables. A test using random subspaces is proposed, which offers higher power when the variables are dependent and is invariant under linear transformations of the marginal distributions. The p-values for the test are obtained using permutations. The test does not rely on assumptions about normality or the structure of the covariance matrix. It is shown by simulation that the new test has higher power than competing tests in realistic settings motivated by microarray gene expression data. Computational aspects of high-dimensional permutation tests are also discussed and an efficient R implementation of the proposed test is provided.

    HSV kategori
    Forskningsprogram
    Matematisk statistik; Statistik
    Identifikatorer
    urn:nbn:se:uu:diva-224136 (URN)10.1016/j.csda.2013.12.003 (DOI)000333781500003 ()
    Tilgjengelig fra: 2014-05-05 Laget: 2014-05-05 Sist oppdatert: 2017-12-05bibliografisk kontrollert
    3. On split sample and randomized confidence intervals for binomial proportions
    Åpne denne publikasjonen i ny fane eller vindu >>On split sample and randomized confidence intervals for binomial proportions
    2014 (engelsk)Inngår i: Statistics and Probability Letters, ISSN 0167-7152, E-ISSN 1879-2103, Vol. 92, s. 65-71Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    We study randomized confidence intervals for binomial proportions, comparing coverage, length and the impact of the randomization. It is seen that the recently proposed split sample intervals can be improved upon in various ways. Criticisms of randomized intervals are discussed.

    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-226502 (URN)10.1016/j.spl.2014.05.005 (DOI)000340313200010 ()
    Tilgjengelig fra: 2014-06-17 Laget: 2014-06-17 Sist oppdatert: 2017-12-05bibliografisk kontrollert
    4. Coverage-adjusted confidence intervals for a binomial proportion
    Åpne denne publikasjonen i ny fane eller vindu >>Coverage-adjusted confidence intervals for a binomial proportion
    2014 (engelsk)Inngår i: Scandinavian Journal of Statistics, ISSN 0303-6898, E-ISSN 1467-9469, Vol. 41, nr 2, s. 291-300Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    We consider the classic problem of interval estimation of a proportion p based on binomial sampling. The ‘exact’ Clopper–Pearson confidence interval for p is known to be unnecessarily conservative. We propose coverage adjustments of the Clopper–Pearson interval that incorporate prior or posterior beliefs into the interval. Using heatmap-type plots for comparing confidence intervals, we show that the coverage-adjusted intervals have satisfying coverage and shorter expected lengths than competing intervals found in the literature.

    HSV kategori
    Forskningsprogram
    Statistik; Matematisk statistik
    Identifikatorer
    urn:nbn:se:uu:diva-224408 (URN)10.1111/sjos.12021 (DOI)000335388400002 ()
    Tilgjengelig fra: 2014-05-12 Laget: 2014-05-12 Sist oppdatert: 2017-12-05bibliografisk kontrollert
    5. The cost of using exact confidence intervals for a binomial proportion
    Åpne denne publikasjonen i ny fane eller vindu >>The cost of using exact confidence intervals for a binomial proportion
    2014 (engelsk)Inngår i: Electronic Journal of Statistics, ISSN 1935-7524, E-ISSN 1935-7524, Vol. 8, s. 817-840Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    When computing a confidence interval for a binomial proportion p one must choose between using an exact interval, which has a coverage probability of at least 1 a for all values of p, and a shorter approximate interval, which may have lower coverage for some p but that on average has coverage equal to 1 a. We investigate the cost of using the exact one and two-sided Clopper-Pearson confidence intervals rat her than shorter approximate intervals, first in terms of increased expected length and then in terms of the increase in sample size required to obtain a desired expected length. Using asymptotic expansions, we also give a closed-form formula for determining the sample size for the exact Clopper-Pearson methods. For two-sided intervals, our investigation reveals an interesting connection between the frequentist Clopper-Pearson interval and Bayesian intervals based on noninformative priors.

    Emneord
    Asymptotic expansion, binomial distribution, confidence interval, expected length, sample size determination, proportion
    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-226501 (URN)10.1214/14-EJS909 (DOI)000338327100001 ()
    Tilgjengelig fra: 2014-06-17 Laget: 2014-06-17 Sist oppdatert: 2017-12-05bibliografisk kontrollert
    6. Exact confidence intervals and hypothesis tests for parameters of discrete distributions
    Åpne denne publikasjonen i ny fane eller vindu >>Exact confidence intervals and hypothesis tests for parameters of discrete distributions
    2017 (engelsk)Inngår i: Bernoulli, ISSN 1350-7265, E-ISSN 1573-9759, Vol. 23, nr 1, s. 479-502Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    We study exact confidence intervals and two-sided hypothesis tests for univariate parameters of stochastically increasing discrete distributions, such as the binomial and Poisson distributions. It is shown that several popular methods for constructing short intervals lack strict nestedness, meaning that accepting a lower confidence level not always will lead to a shorter confidence interval. These intervals correspond to a class of tests that are shown to assign differing p-values to indistinguishable models. Finally, we show that among strictly nested intervals, fiducial intervals, including the Clopper-Pearson interval for a binomial proportion and the Garwood interval for a Poisson mean, are optimal.

    Emneord
    binomial distribution, confidence interval, expected length, fiducial interval, hypothesis test, Poisson distribution
    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-229398 (URN)10.3150/15-BEJ750 (DOI)000389565500017 ()
    Tilgjengelig fra: 2014-08-06 Laget: 2014-08-06 Sist oppdatert: 2017-12-05bibliografisk kontrollert
  • 227.
    Thulin, Måns
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Tillämpad matematik och statistik.
    On split sample and randomized confidence intervals for binomial proportions2014Inngår i: Statistics and Probability Letters, ISSN 0167-7152, E-ISSN 1879-2103, Vol. 92, s. 65-71Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We study randomized confidence intervals for binomial proportions, comparing coverage, length and the impact of the randomization. It is seen that the recently proposed split sample intervals can be improved upon in various ways. Criticisms of randomized intervals are discussed.

  • 228.
    Thulin, Måns
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Tillämpad matematik och statistik.
    Tests for multivariate normality based on canonical correlations2014Inngår i: Statistical Methods & Applications, ISSN 1618-2510, Vol. 23, nr 2, s. 189-208Artikkel i tidsskrift (Fagfellevurdert)
  • 229.
    Thulin, Måns
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Tillämpad matematik och statistik.
    The cost of using exact confidence intervals for a binomial proportion2014Inngår i: Electronic Journal of Statistics, ISSN 1935-7524, E-ISSN 1935-7524, Vol. 8, s. 817-840Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    When computing a confidence interval for a binomial proportion p one must choose between using an exact interval, which has a coverage probability of at least 1 a for all values of p, and a shorter approximate interval, which may have lower coverage for some p but that on average has coverage equal to 1 a. We investigate the cost of using the exact one and two-sided Clopper-Pearson confidence intervals rat her than shorter approximate intervals, first in terms of increased expected length and then in terms of the increase in sample size required to obtain a desired expected length. Using asymptotic expansions, we also give a closed-form formula for determining the sample size for the exact Clopper-Pearson methods. For two-sided intervals, our investigation reveals an interesting connection between the frequentist Clopper-Pearson interval and Bayesian intervals based on noninformative priors.

  • 230.
    Thulin, Måns
    et al.
    Uppsala universitet, Humanistisk-samhällsvetenskapliga vetenskapsområdet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    Zwanzig, Silvelyn
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Tillämpad matematik och statistik.
    Exact confidence intervals and hypothesis tests for parameters of discrete distributions2017Inngår i: Bernoulli, ISSN 1350-7265, E-ISSN 1573-9759, Vol. 23, nr 1, s. 479-502Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We study exact confidence intervals and two-sided hypothesis tests for univariate parameters of stochastically increasing discrete distributions, such as the binomial and Poisson distributions. It is shown that several popular methods for constructing short intervals lack strict nestedness, meaning that accepting a lower confidence level not always will lead to a shorter confidence interval. These intervals correspond to a class of tests that are shown to assign differing p-values to indistinguishable models. Finally, we show that among strictly nested intervals, fiducial intervals, including the Clopper-Pearson interval for a binomial proportion and the Garwood interval for a Poisson mean, are optimal.

  • 231.
    Tsvetkova, Milena
    et al.
    Univ Oxford, Oxford Internet Inst, 1 St Giles, Oxford OX1 3JS, England..
    Nilsson, Olof
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Tillämpad matematik och statistik.
    Öhman, Camilla
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Tillämpad matematik och statistik.
    Sumpter, Lovisa
    Stockholm Univ, Dept Math & Sci Educ, S-10691 Stockholm, Sweden..
    Sumpter, David
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Tillämpad matematik och statistik.
    An experimental study of segregation mechanisms2016Inngår i: EPJ DATA SCIENCE, ISSN 2193-1127, Vol. 5, artikkel-id 4Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Segregation is widespread in all realms of human society. Several influential studies have argued that intolerance is not a prerequisite for a segregated society, and that segregation can arise even when people generally prefer diversity. We investigated this paradox experimentally, by letting groups of high-school students play four different real-time interactive games. Incentives for neighbor similarity produced segregation, but incentives for neighbor dissimilarity and neighborhood diversity prevented it. The participants continued to move while their game scores were below optimal, but their individual moves did not consistently take them to the best alternative position. These small differences between human and simulated agents produced different segregation patterns than previously predicted, thus challenging conclusions about segregation arising from these models.

  • 232.
    Tucker, Warwick
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Analys och tillämpad matematik. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Tillämpad matematik och statistik.
    Computer-Aided Proofs via Interval Analysis2015Inngår i: The Princeton Companion to Applied Mathematics / [ed] Nicholas J. Higham, Princeton University Press, 2015, s. 790-795Kapittel i bok, del av antologi (Fagfellevurdert)
  • 233.
    Tucker, Warwick
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Analys och tillämpad matematik. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Tillämpad matematik och statistik.
    Interval Analysis2015Inngår i: The Princeton Companion to Applied Mathematics / [ed] Nicholas J. Higham, Princeton University Press, 2015, s. 105-106Kapittel i bok, del av antologi (Fagfellevurdert)
  • 234.
    Tucker, Warwick
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Analys och tillämpad matematik. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Tillämpad matematik och statistik.
    Interval Methods2015Inngår i: Uncertainty in Biology: A Computational Modeling Approach / [ed] Liesbet Geris and David Gomez-Cabrero, Springer Publishing Company, 2015, s. 99-211Kapittel i bok, del av antologi (Fagfellevurdert)
  • 235.
    Vaicenavicius, Juozas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Tillämpad matematik och statistik.
    Asset liquidation under drift uncertainty and regime-switching volatilityArtikkel i tidsskrift (Annet vitenskapelig)
    Abstract [en]

    Optimal liquidation of an asset with unknown constant drift and stochastic regime-switching volatility is studied. The uncertainty about the drift is represented by an arbitrary probability distribution, the stochastic volatility is modelled by m-state Markov chain. Using filtering theory, an equivalent reformulation of the original problem as a four-dimensional optimal stopping problem is found and then analysed by constructing approximating sequences of three-dimensional optimal stopping problems. An optimal liquidation strategy and various structural properties of the problem are determined. Analysis of the two-point prior case is presented in detail, building on which, an outline of the extension to the general prior case is given.

  • 236.
    Vallin, Filip
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Tillämpad matematik och statistik.
    Auction theory2019Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
  • 237. van den Berg, J.
    et al.
    Björnberg, Jakob E.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Tillämpad matematik och statistik.
    Heydenreichd, M.
    Sharpness versus robustness of the percolation transition in 2d contact processes2015Inngår i: Stochastic Processes and their Applications, ISSN 0304-4149, E-ISSN 1879-209X, Vol. 125, nr 2, s. 513-537Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We study versions of the contact process with three states, and with infections occurring at a rate depending on the overall infection density. Motivated by a model described in Kefi et al. (2007) for vegetation patterns in arid landscapes, we focus on percolation under invariant measures of such processes. We prove that the percolation transition is sharp (for one of our models this requires a reasonable assumption). This is shown to contradict a form of 'robust critical behaviour' with power law cluster size distribution for a range of parameter values, as suggested in Kefi et al. (2007). 

  • 238.
    Vedin, Oskar
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Tillämpad matematik och statistik.
    Sakförsäkring och approximation av totalt skadebelopp2017Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
  • 239.
    Veselinović, Katarina
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Tillämpad matematik och statistik.
    Optimal margin levels in Gaussian environments2018Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
  • 240.
    Wang, Peiyu
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Tillämpad matematik och statistik.
    Liquidity Adjusted Value-at-Risk and Its Applications2017Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
  • 241.
    Wang, Yuqiong
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Tillämpad matematik och statistik.
    Optimal Stopping with Discrete Costly Observations2018Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
  • 242.
    Ward, Ashley J. W.
    et al.
    Univ Sydney, Sch Life & Environm Sci, Sydney, NSW, Australia..
    Schaerf, Timothy M.
    Univ Sydney, Sch Life & Environm Sci, Sydney, NSW, Australia.;Univ New England, Sch Sci & Technol, Armidale, NSW, Australia..
    Herbert-Read, James E.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Tillämpad matematik och statistik. Stockholm Univ, Dept Biol, Stockholm, Sweden..
    Morrell, Lesley
    Univ Hull, Sch Biol Biomed & Environm Sci, Kingston Upon Hull, N Humberside, England..
    Sumpter, David J. T.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Tillämpad matematik och statistik.
    Webster, Mike M.
    Univ St Andrews, Sch Biol, St Andrews, Fife, Scotland..
    Local interactions and global properties of wild, free-ranging stickleback shoals2017Inngår i: Royal Society Open Science, E-ISSN 2054-5703, Vol. 4, nr 7, artikkel-id 170043Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Collective motion describes the global properties of moving groups of animals and the self-organized, coordinated patterns of individual behaviour that produce them. We examined the group-level patterns and local interactions between individuals in wild, free-ranging shoals of three-spine sticklebacks, Gasterosteus aculeatus. Our data reveal that the highest frequencies of near-neighbour encounters occur at between one and two body lengths from a focal fish, with the peak frequency alongside a focal individual. Fish also show the highest alignment with these laterally placed individuals, and generally with animals in front of themselves. Furthermore, fish are more closely matched in size, speed and orientation to their near neighbours than to more distant neighbours, indicating local organization within groups. Among the group-level properties reported here, we find that polarization is strongly influenced by group speed, but also the variation in speed among individuals and the nearest neighbour distances of group members. While we find no relationship between group order and group size, we do find that larger groups tend to have lower nearest neighbour distances, which in turn may be important in maintaining group order.

  • 243.
    Wennerberg, Anders
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Tillämpad matematik och statistik.
    Livförsäkring – Från ränta till Thieles differentialekvation2019Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
  • 244.
    Westerberg, Marcus
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Tillämpad matematik och statistik.
    Diagnosing Metastatic Prostate Cancer Using PSA:A Register-Based Cohort Study with Missing Data2017Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
  • 245.
    Westerberg, Marcus
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Tillämpad matematik och statistik.
    Reasons for Missing Data of Risk Categorisation in NPCR2015Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
    Abstract [en]

    The risk of prostate cancer (PCa) can be described using ve risk categories based on clinicalassessment involving the risk of cancer and metastasis level. In some cases the information neededto calculate the risk is not registered. The aim is to assess potential dierences in properties likeage, treatment, comorbidity and survival, between men with a dened risk stage categorisation ofprostate cancer compared to men lacking information to calculate the risk stage category. Themain measures involved in the risk stage assessment are Gleason score, prostate specic antigen(PSA) value and T-stage. Men missing data for risk stage categorisation may be lacking one of thethree or a combination of at least two out of the three. Subgroups of these men will be analysedin a similar way, in order to understand the reasons to why they are missing data for risk stagecategorization.Statistical analysis involves univariate and multivariate logistic regression, along with survivaland competing risk analysis. Data will be presented in tables, gures and forest plots, includingodds ratios, 95% condence intervals and p-values.According to the study, men missing data of risk stage categorization were about 2.6% of allmen in the data base, and had most likely a low risk PCa. They had higher comorbidity levelsbut the overall probability of death was the same compared to other men. In addition, they hadsignicantly lower proportion of death by PCa and experienced a large proportion of death byother cancer, which concurs with the previous conclusions about comorbidity and low risk PCa,indicating that they had another disease, possibly cancer, that required more attention.Considering only men missing data for risk categorisation, a large proportion were missingPSA level (58.3%), and these men had higher comorbidity, were older, and had a large proportionof death by other cancer. Surprisingly, men missing Gleason level (20.3%) had increased oddsratios for lower comorbidity levels, were younger at time of diagnosis, and had a higher survivalprobability in general. Unexpectedly, men missing T-stage (32%) were more likely to being treatedby Radio Theraphy (RT), were less likely to attend university hospitals and more likely to attendprivate physicians. Men missing a combination of at least two out of three of Gleason, PSA, T-stage(19.6%) had higher comorbidity levels and were more likely to be treated by RT, less likely to attenduniversity hospitals, had a large proportion of death by other cancer, and a larger proportion ofdeath closer to the time of diagnosis.Lastly, there were some indications of variations of the proportions of missing data of riskstage categorisation when dividing it into the subgroups mentioned above, and viewed over year ofdiagnosis. There was an increase in missing data of risk stage categorization around 2006 and anexplanation of this could be the change of IT-system for registration, leaving a general increase ofmissing data behind it, perhaps due to a looser control during the transition and unfamiliarity ofthe new system.The main conclusion was that the reasons for missing data of risk stage categorisation are mostlikely high comorbidity levels, probably including another cancer in combination with a low riskPCa. It was most common to be missing data of risk stage categorisation due to missing PSAlevel, and those men had high comorbidity and were older. Surprisingly, private physicians and/ortreatment by RT were more likely to be missing T-stage, and younger men with low comorbiditywere more likely to be missing Gleason score.

  • 246. Westerlund, Joakim
    et al.
    Larsson, Rolf
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Tillämpad matematik och statistik.
    New tools for understanding the local asymptotic power of panel unit root tests2015Inngår i: Journal of Econometrics, ISSN 0304-4076, E-ISSN 1872-6895, Vol. 188, nr 1, s. 59-93Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Motivated by the previously documented discrepancy between actual and predicted power, the present paper provides new tools for analyzing the local asymptotic power of panel unit root tests. These tools are appropriate in general when considering panel data with a dominant autoregressive root of the form rho(i)= 1 + ciN(-k)T(-tau), where i = 1,..., N indexes the cross-sectional units, T is the number of time periods and ci is a random local-to-unity parameter. A limit theory for the sample moments of such panel data is developed and is shown to involve infinite-order series expansions in the moments of ch in which existing theories can be seen as mere first-order approximations. The new theory is applied to study the asymptotic local power functions of some known test statistics for a unit root. These functions can be expressed in terms of the expansions in the moments of ci, and include existing local power functions as special cases. Monte Carlo evidence is provided to suggest that the new results go a long way toward bridging the gap between actual and predicted power.

  • 247.
    Wiklund, Tilo
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Tillämpad matematik och statistik.
    The Deficiency Introduced by Resampling2018Inngår i: Mathematical Methods of Statistics, ISSN 1066-5307, E-ISSN 1934-8045, Vol. 27, nr 2, s. 145-161Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    When the classical nonparametric bootstrap is implemented by a Monte-Carlo procedure one resamples values from a sequence of, typically, independent and identically distributed ones. But what happens when a decision has to be taken based on such resampled values? One way to quantify the loss of information due to this resampling step is to consider the deficiency distance, in the sense of Le Cam, between a statistical experiment of n independent and identically distributed observations and the one consisting of m observations taken from the original n by resampling with replacement. By comparing with an experiment where only subsamplingwith a random subsampling size has been performed one can bound the deficiency in terms of the amount of information contained in additional observations. It follows for certain experiments that the deficiency distance is proportional to the expected fraction of observations missed when resampling.

  • 248.
    Yilmaz, Bertan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Tillämpad matematik och statistik.
    Customer Analytics and Cluster Analysis: A Clustering Application for CustomerSegmentation Based on CX Data2019Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave