Empirically Defined Health States for Depression from the SF-12

The authors attempt to define objectively and describe a set of clinically relevant health states that encompass the typical effects of depression on quality of life in an actual patient population. Their model was designed to facilitate the elicitation of patients' and the public's values (utilities) for outcomes of depression. Data were taken from the depression panel of the Medical Outcomes Study. Data include scores on the 12-Item Short Form Health Survey (SF-12) as well as independently obtained diagnoses of depression for 716 patients. Follow-up information, one year after baseline, was available for 166 of these patients. The authors find, on the basis of a combination of statistical and clinical criteria, that six states are optimal for summarizing the range of health experienced by depressed patients. Each state is described in terms of a subject who is typical in a sense that is articulated with the cluster-analytic approach. In all of the models, the relationship between health state membership and clinical diagnosis is highly statistically significant. The models are also sensitive to changes in patients' clinical status over time. The authors conclude that cluster analysis is demonstrably a powerful methodology for forming clinically valid health states from health status data. The states produced are suitable for the experimental elicitation of preference and analyses of costs and utilities.