Outcome Measurement and Service Evaluation--A Note on Research Design

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Summary The purpose of this research note is to demonstrate how an individualized quality of life instrument could be adapted to provide a more accurate estimate of the impact of a social service on a person's quality of life. An increase in quality of life between the start and end of a service is often taken as an indication that the service impacted positively on quality of life. The modifications to the quality of life instrument sug gested in this paper show that this assumption is not always accurate and should be questioned directly. Research into the effectiveness of social services often unavoidably lacks a high degree of internal validity due to, for example, ethical, financial or operational con cerns. Research designs in this area frequently take the form of cohort studies or before-and-after studies, where allocation of clients to the treatment group is not influenced by the fact that a research study is being conducted. The advantage of such designs is that they are high in external, and more specifically, ecological validity (phenomena are studied in their 'natural' environment and therefore the research setting is low in artificiality). However, the disadvantage lies in the inability of such designs to provide accurate information about the effect of a service on an outcome of interest. Therefore, when using such research designs, it is incumbent on researchers to gather information that will enable the closest possible estimation of the nature of any cause and effect relationships between service and outcome. This research note demonstrates how an instrument designed to measure individu alized quality of life—the Patient Generated Index (Ruta et al, 1994)—can be