Validity of SF-12 summary scores in a Greek general population

Abstract

BACKGROUND: The 12-item Health Survey (SF-12) was developed as a shorter alternative to the SF-36 for use in large-scale studies, particularly when overall physical and mental health are the outcomes of interest instead of the typical eight-scale profile. The main purpose of this study was to assess the validity of the Greek version of the SF-12. METHODS: A stratified representative sample (N = 1005) of the Greek general population was interviewed. The survey included the SF-36, the EQ-5D and questions on socio-demographic and health-related characteristics. SF-12 summary scores were derived using the standard US algorithm. Factor analysis was used to confirm the hypothesized component structure of the SF-12 items. Construct validity was investigated with "known groups" validity testing and via convergent and divergent validity, which in turn were assessed by the correlations with the EQ-5D dimensions. Concurrent validity was assessed by comparisons with SF-36 summary scores. RESULTS: SF-12 summary scores distinguished well, and in the expected manner, between groups of respondents on the basis of gender, age, education, socio-economic status, self-reported health problems and health services utilization, thus providing evidence of construct validity. Effect size differences between SF-36 and SF-12 summary scores were generally small (<0.2), supporting concurrent (criterion) validity. Significantly lower mean PCS-12 and MCS-12 scores were observed for respondents reporting chronic conditions compared to those without (P < 0.001). Convergent and divergent validity were supported by expected relationships with the EQ-5D. Reporting a problem in an EQ dimension was associated with lower SF-12 summary scores, supporting concurrent validity. Sensitivity of the Greek SF-12 and replication of the original measurement and conceptual model were demonstrated. CONCLUSION: The results provide evidence on the validity of the Greek SF-12 and, in conjunction to future studies addressing test-retest reliability and responsiveness, support its use in Greek health status studies as a brief, yet valid, alternative to the SF-36.