HETEROGENEITY IN THE RELATIONSHIP BETWEEN THE TIME TRADEOFF AND SHORTFORM-36 FOR HIV-INFECTED AND PRIMARY-CARE PATIENTS

OBJECTIVES. Evidence in the literature suggests that the overall corre lation between descriptive and valuational measures of health are weak to moderate. In this study, the relationship between descriptive heal th status measures, obtained using the Short-Form 36, and health value s, measured with the time tradeoff, was explored. METHODS. Two groups of patients matched for age and gender were interviewed. One group com prised 139 human immunodeficiency virus (HIV)-infected patients; the o ther group comprised 124 primary care patients. The relationship betwe en the SF-36 and the time tradeoff was estimated, assuming homogeneity across patients, using multiple regression analysis. Subsequently, th e relationship was examined assuming heterogeneity across patients and using the expectation maximization algorithm in a maximum likelihood context (latent class analysis). RESULTS. Four classes, representing 4 7%, 13%, 8%, and 32% of the population, respectively, were found. The overall percentage of variation explained under the assumption of a ho mogeneous relationship was only 33% as compared with 85% when heteroge neity was accounted for. Only three characteristics (educational level , employment status, and the SF-36 social functioning score) sufficed to generate a nearly perfect classification of the patients. CONCLUSIO NS. Heterogeneity across subjects should be taken into account in desc ribing the relationship between health values and health status dimens ions. Key words: health status measure; health utility measure; latent class analysis; heterogeneity. (Med Care 1998;36:523-532)