Integrating Models of Disability: A reply to Shakespeare and Watson

The WHO model has been widely used as a model of disability and continues to be the implicit model adopted in the delivery of health care. The model has been criticised in a variety of ways with resulting suggestions that it can be modified or abandoned. However the model offers a useful staring point by clearly separating the concepts of ‘impairment’ (limitations in the performance of activities). The model proposes that disability is the result of impairment, but opens up the possibility that other factors may also influence disability. Clarification of these other factors is essential to the viability of this model. Since disability is defined in behavioural terms, it seems obvious that disability should be influenced by the same variables as influence other behaviours, including physiological, environmental, social, cognitive and emotional factors. I have proposed (Johnston, 1996a) that it is possible to integrate the WHO model with some of the current most strongly validated theories of behaviour. Based on findin gs from observational, longitudinal and experimental studies, perceptions of control have been found to determine levels of disability, even allowing for level of impairment. For example, one experimental study showed that when individuals were asked to describe occasions when they found it difficult to exercise control, their perceptions of control were reduced and their levels of disability were increased; similarly, describing occasions of successful control resulted in greater perceived control and less disability (Fisher and Johnston, 1996). This study clearly demonstrates changes in disability without changes in impairment and thus challenges the WHO model. I have proposed that, rather than abandoning the WHO model, it should be developed to be more compatible with existing scientific findings and have proposed a fuller model of factors explaining limitations in functional activities. Other psychological models deal with the psychological and emotional consequences rather than determinants of impairment and disability.