Disability, epidemiological studies, and contextual factors

This thesis is composed of several related pieces of work. Based on the WHO's International Classification of Functioning, Disability, and Health (ICF) conceptual model, it examines how the relationships between activity limitation and participation restriction are influenced by contextual factors. This dissertation suggests that contextual factors can act in four ways in the relationship between activity limitation and participation restriction. The four roles can be described as independent effects, mediating effects, confounding effects, and moderating effects. This work is extended to explore critically the concepts of confounding, mediating, and moderating factors, which has important implications in epidemiological studies. Finally, this thesis presents two empirical examples of mediating effects in the context of employment and perceived level of independence.; As a contribution to theoretical epidemiology, this thesis draws upon the concepts and methods from other disciplines and explores how a two variable relationship (X → Y) can be affected by a third variable. As a result, the concept of a "confounding factor" has been decomposed into 5 conceptually dissimilar factors: (1) correlated confounding factor; (2) design introduced confounding factor; (3) opportunistic confounding factor; (4) full common causal confounding; and (5) partial common causal confounding factor. Similarly, the concept of moderating factor has also been scrutinized and classified into four types: mutual, contingent moderating, conjoint moderating, responsive moderating factors. Empirical examples are provided for each of the terms. Statistical simulations were performed to further corroborate the cases of the full and partial common casual confounding factors.; Two separate empirical studies, (perceived independence and labour force participation) were carried out to show how the hypothesized contextual factors affect the participation of people with activity limitations. The results suggest that people's coping efficacy and perceived need for workplace accommodation act as important modifiable mediating factors between activity limitation and participation restriction (perceived independence and labour force participation).