In this paper I present an analysis of how disability is defined in a sample of often referred works on disability. The analysis focuses on how disability is defined, both explicit and implicit in the selected works. In short, the findings suggest that all of them, but of various extents, lack from consistency in the definition of disability. Expressed in a quantitative methodological vocabulary, one can say that the validity is violated in the analyzed studies.
This inconsistency, or validity violation, appears in three different modes. First, there is a traditional kind of validity, where the theoretical and operational definitions differ from each other. Second, some of the studies lack from what can be called internal coherency, where the author uses the concept of disability in altered ways through her/his text. The third and last inconsistency has to do with referential techniques. Commenting citations, it is not uncommon that the authors retain conceptualizations originating from the quoted
sources. In some of the texts, this engenders a definitional opaqueness. However, since disability is such an ambiguous concept, the findings question the possibility to apply a
strict criterion of validity to studies on disability. Nevertheless, there is a need for some kind of expressed declaration of how the concept will be used.