Increasingly, tied to factors such as increased emphasis on accountability and health care spending restraints, occupational therapists are required to implement evidence-based practice. When implementing evidence-based assessment, it is critical that occupational therapists examine and challenge some of the assumptions underlying the current use of measures, as well as the conclusions being drawn from their use. In order to most effectively judge the appropriateness of measures informing their assessments, interventions and recommendations, occupational therapists must draw upon measurement theory and concepts. To date, occupational therapy literature has predominantly emphasized a narrow conceptualization of validity that focuses on empirical evidence. The work of Samuel Messick provides a more comprehensive framework of construct validity that considers both empirical and ethical issues. This framework binds the social consequences of assessment to the evidential basis of test interpretation and use, and challenges occupational therapists to broaden their consideration of validity by addressing both ethical and empirical issues when choosing measures.