Assessing function and functional outcome in schizophrenia.

The diagnosis of schizophrenia can only be made in the presence of a loss of functioning in domains such as employment, independent living, and social functioning. Accurately measuring functioning is central to research on the course of the disorder, treatment and rehabilitation outcomes, and biosocial factors in schizophrenia. Assessments of functional disability have described three dimensions of functioning: functional capacity, functional performance, and functional outcome. The "competence/performance" distinction refers to the observation that an individual may demonstrate an ability to perform a functional task (capacity) but may not do so in her own community environment (performance). Functional outcomes are the result of both capacity and performance. Several recent reviews have compared the characteristics, reliability, and validity of various functional assessment instruments. Two major initiatives are underway to gather additional comparative data about functional assessment strategies. Recently, both the recovery movement and the recognition of the role of environmental factors in functioning have raised questions about the conceptual content of the functioning construct (construct validity). For instance, several studies have demonstrated that features of functioning need not track together over the course of the illness. In addition, the notion of recovery emphasizes processes like community integration and subjective well-being that are not static outcomes but are continually evolving features of the life course in chronic illness. Findings on the dynamic role of environmental moderators such as support and opportunity also present challenges to scientific constructs. For these reasons and others, the ecological validity of functional assessments has become a central concern. Both the verisimilitude and veridicality of functional assessments can be empirically assessed, but to date very few studies have measured the extent to which functional measures accurately predict individuals' behavior in their usual environments. Observational studies in naturalistic environments are one important area for future research.