THEORY AND METHODS Retest reliability of surveillance questions on health related quality of life

Study objectives: Health related quality of life (HRQoL) is an important surveillance measure for monitoring the health of populations, as proposed in the American public health plan, Healthy People 2010. The authors investigated the retest reliability of four HRQoL questions from the US Behavioral Risk Factor Surveillance System (BRFSS). Design: Randomly sampled BRFSS respondents from the state of Missouri were re-contacted for a retest of the HRQoL questions. Reliability was estimated by κ statistics for categorical questions and intraclass correlation coefficients for continuous questions. Setting: Missouri, United States. Participants: 868 respondents were re-interviewed by telephone about two weeks after the initial interview (mean 13.5 days). Participants represented the adult, non-institutionalised population of Missouri: 59.1% women; mean age 49.5 years; 93.2% white race. Main results: Retest reliability was excellent (0.75 or higher) for Self-Reported Health and Healthy Days measures, and moderate (0.58 to 0.71) for other measures. Reliability was lower for older adults. Other demographic subgroups (for example, gender) showed no regular pattern of differing reliability and there was very little change in reliability by the time interval between the first and second interview. Conclusions: Retest reliability of the HRQoL Core is moderate to excellent. Scaling options will require future attention, as will research into appropriate metrics for what constitutes important population group differences and change in HRQoL.