Research

Comparing the SF-12 and SF-36 health status questionnaires in patients with and without obesity

Christina C Wee , Roger B Davis and Mary Beth Hamel

Division of General Medicine and Primary Care, Department of Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts, USA

author email corresponding author email

Health and Quality of Life Outcomes 2008, 6:11doi:10.1186/1477-7525-6-11

Published:	30 January 2008

Abstract

Objective

To assess how well the SF-36, a well-validated generic quality of life (QOL) instrument, compares with its shorter adaptation, the SF-12, in capturing differences in QOL among patients with and without obesity.

Methods

We compared the correlation between the physical (PCS) and mental (MCS) component summary measures of the SF-12 and SF-36 among 356 primary care patients using Pearson coefficients (r) and conducted linear regression models to see how these summary measures captures the variation across BMI. We used model R² to assess qualitatively how well each measure explained the variation across BMI.

Results

Correlations between SF-12 and SF-36 were higher for the PCS in obese (r = 0.89) compared to overweight (r = 0.73) and normal weight patients (r = 0.75), p < 0.001, but were similar for the MCS across BMI. Compared to normal weight patients, obese patients scored 8.8 points lower on the PCS-12 and 5.7 points lower on the PCS-36 after adjustment for age, sex, and race; the model R² was higher with PCS-12 (R² = 0.22) than with PCS-36 (R² = 0.16). BMI was not significantly associated with either the MCS-12 or MCS-36.

Conclusion

The SF-12 correlated highly with SF-36 in obese and non-obese patients and appeared to be a better measure of differences in QOL associated with BMI.