Measuring sexual risk for HIV: a Rasch scaling approach.

In this study, we developed an HIV transmission risk scale and examined its psychometric properties using data on sexual behavior obtained from a probability sample of adult men who have sex with men living in Chicago. We used Messick's (Am Psychol 50:741-749, 1995) conceptualization of unified validity theory to organize the psychometric properties of data. Evidence related to scale content was investigated via Rasch item fit statistics, point-measure correlations, and expert evaluation. The substantive aspect of validity was addressed by interpreting the meaningfulness of the item difficulty hierarchy (continuum of risky behaviors) and assessment of person fit. The structural aspect of validity was assessed using Rasch item fit statistics, principal component analysis of standardized residuals, and other residual analyses. The generalizability aspect of validity was investigated via internal consistency reliability estimates for both items and persons, and aspects of external validity were addressed by examining between-group differences with respect to levels of risky behavior. Applications and suggested future studies are discussed.