A PERCEIVED HEALTH INDEX FOR USE IN PERSONS WITH ADVANCED HIV DISEASE- DERIVATION, RELIABILITY, AND VALIDITY

Acceptance of health status as an outcome in clinical trials of new tr eatments for HIV disease has been hampered by the lack of valid and cl inically relevant means of summarizing differences across multiple dim ensions. We formed a summary Perceived Health Index from health status measures adapted from RAND Medical Outcomes Study scale and contained in the HIV-PARSE survey instrument, which had been administered to a large number of participants in clinical trials for advanced HIV disea se. The psychometric properties of the included health status scales w ere assessed using multitrait scaling and test-retest stability. Weigh ts for the index were derived from regressions of Current Health Perce ptions on the domain-specific health status scales. The effect of part icipant characteristics on weights was tested. Finally, the reliabilit y and known-clinical groups validity of the index was assessed. Data w ere obtained from 1,862 clinical trial participants who provided a tot al of 7,352 observations. The mean CD4 count was 131. The internal con sistency reliability of the multi-item scales ranged from 0.86 to 0.90 , and items demonstrated excellent discrimination across scales. The d omain-specific scales explained 59% of the variation in the Current He alth Perceptions scale (P <0.00001). The resulting Perceived Health In dex was equal to 0.20 Physical Functioning + 0.15 Pain + 0.41 Energy/F atigue + 0.10 Emotional Well-Being + 0.05 Social Functioning + 0.09 Ro le Functioning. The strong positive bivariate relationship between the Cognitive Function/Distress scale and the Current Health Perceptions scale was subsumed by the combination of the other domain-specific sca les in multiple regressions, so it does not appear independently in th e index. The proportional weights used in the index were insensitive t o variations in demographics. The reliability of the index was conserv atively estimated to be 0.94. Patients with index scores in the lowest quartile had a 2- to 11-fold higher probability than those in the hig hest quartile of reporting various specific clinical events, and the i ndex correlated significantly more highly with the number of such even ts than did the current health perceptions scale. The modified MOS hea lth status scales included in the HIV-PARSE are reliable and valid in patients with advanced HIV disease. The Perceived Health Index provide s a reliable and valid means of summarizing self-reported current heal th, correlates strongly with clinical indicators, and should be useful as a outcome measure in patients enrolling into clinical trials of th erapies for advanced HIV disease. Regression based weights are a usefu l means of summarizing multidimensional measures.