Different factor loadings for SF36: The Strong Heart Study and the National Survey of Functional Health Status

BackgroundTo increase our understanding of the psychometric characteristics and factor structure of the SF36® in older American Indian populations.MethodsBetween 1993 and 1995, SF36® data were collected from 3,488 Phase II participants of the Strong Heart Study (SHS) between the ages of 48 and 81. Comparison data were provided by an age- and gender-matched sample (n = 695) from the National Survey of Functional Health Status (NSFHS) conducted in 1989 and 1990.ResultsGenerally, the basic psychometric analyses showed that the SF36® performed adequately in these older American Indians. Exploratory factor analyses indicated that a one-factor model best fit the data for both older groups. On the other hand, confirmatory factor analyses showed that a two-factor model with correlated factors provided a superior fit to the data than a one-factor model. An assumption of equivalent factor loadings for the SHS and NSFHS groups was untenable.ConclusionThese analyses demonstrate that use of summary scores assuming a differentiated physical/mental functioning structure is likely improper in at least some populations. The SF36® provides an important opportunity to understand cultural differences in the conceptualization and measurement of health-related quality of life.