Conceptual and measurement models of disability
Numerous theoretical frameworks have been applied to further our understanding of the correlates, causes and consequences of disability, and each is accompanied by a particular conceptualisation of disability. In this thesis, disability was conceptualised as behaviour. The concept of disability as behaviour is accompanied by psychological theories of behaviour and behaviour change within which behaviour is viewed as a product of motivational factors. A repertory grid study indicated that people with mobility disability use motivational concepts to distinguish between physical activities typically used to index their disability. These data lent support to the suitability of the disability as behaviour concept in this population. Consequently, psychological theory, in the form of the theory of planned behaviour (TPB) and social cognitive theory (SCT), was used to account for walking disability in an orthopaedic sample. The empirical application of psychological theories requires the operationalisation of the constructs within those theories. An investigation of the content validity of existing measures of the perceived control constructs from the TPB and SCT indicated current measurement items do not show discriminant content validity. These data were used to select perceived control items into the study of disability in an orthopaedic sample. The content validity of the perceived control items was investigated using confirmatory factor analyses applied to the responses of the orthopaedic sample. Structural equation modelling indicated that both the TPB and SCT could account for walking disability in the orthopaedic sample. Finally, the ability of the TPB and SCT to mediate between the central constructs of the main medical model of disability, namely the International Classification of Functioning Disability and Health (ICF), was assessed using structural modelling. This integrated model accounted for a greater proportion of the variance in walking disability than did the ICF alone, suggesting psychological theory can be used to improve the ICF model.