Validation and calibration of the SF-36 health transition question against an external criterion of clinical change in health status

Cross-sectional surveys depend on retrospective health transition questions (HTQ) to estimate recent changes in health status. This paper assesses the validity of the SF-36 HTQ and calibrates its categories against change assessed prospectively on the SF-36 domain scales in a sub-group known to have experienced clinically important changes in health status. Adults (n = 9,649) from a longitudinal population survey completed the SF-36 in 2001 and 2002. Prospective measures were calculated as mean changes in SF-36 scale scores adjusted for age and gender, and also expressed as standardised response means. Comparison groups were those who had developed a long-term health condition since the last interview and the HTQ response categories for those who had not developed any new conditions. Those with a new condition and those without a new condition but who described their health as somewhat worse than a year ago had comparable declines in health status on all domain scales except role physical, where those with a new condition experienced a greater decline. This analysis demonstrates the validity and limitations of the HTQ as a measure of change in population studies. The calibration is useful for interpreting the meaning of the HTQ categories at the group level but not at the individual level.