A shorter form health survey: can the SF-12 replicate results from the SF-36 in longitudinal studies?

The SF-36 is a generic health status measure which has gained popularity as a measure of outcome in a wide variety of patient groups and social surveys. However, there is a need for even shorter measures, which reduce respondent burden. The developers of the SF-36 have consequently suggested that a 12-item sub-set of the items may accurately reproduce the two summary component scores which can be derived from the SF-36 [the Physical Component Summary Score (PCS) and Mental Health Component Summary Score (MCS)]. In this paper, we adopt scoring algorithms for the UK SF-36 and SF-12 summary scores to evaluate the picture of change gained in various treatment groups. The SF-36 was administered in three treatment groups (ACE inhibitors for congestive heart failure, continuous positive airways therapy for sleep apnoea, and open vs laparoscopic surgery for inguinal hernia). PCS and MCS scores calculated from the SF-36 or a sub-set of 12 items (the 'SF-12') were virtually identical, and indicated the same magnitude of ill-health and degree of change over time. The results suggest that where two summary scores of health status are adequate than the SF-12 may be the instrument of choice.