Session number: 1046
Abstract title: Comparison of the SF-36 and SF-12 Summary Scales in a Veteran Population
Author(s):
MB McDonell - VA Puget Sound Health Care System, HSR&D
S Hedrick - VA Puget Sound Health Care System, HSR&D and University of Washington, Department of Health Services
SD Fihn - VA Puget Sound Health Care System, HSR&D and University of Washington, Department of Medicine
Objectives: Self-reported health status is collected for many reasons, and patients are often asked to complete multiple questionnaires. Shorter surveys are attractive to reduce respondent burden, but only if information loss is minimal. We compared longitudinal responses to SF-36 and SF-12 summary measures in a group of veterans receiving primary care using baseline, 1 year, and change scores.
Methods: Data were collected as part of ACQUIP, a group-randomized trial conducted in primary care clinics at 7 VAs. 4257 intervention patients who completed the SF-36 at baseline and one year were included. Physical and mental summary scores were calculated using SF-36 (PCS36 and MCS36) and standard SF-12 scoring algorithms (PCS12 and MCS12). Change scores were computed. Descriptive statistics, including means, standard deviations and scores at selected percentiles for summary measures were compared.
Results: Mean PCS36 scores at baseline and one-year were 34.3 (sd 11.8) and 33.7 (sd 12.4) respectively, compared to 34.8 (sd 11.0)and 34.4 (sd 11.5) for PCS12. Mean MCS36 scores at baseline and 1-year were 46.9 (sd 12.8) and 48.0 (sd 12.8) respectively, compared to 46.8 (sd 12.0)and 47.6 (sd 12.0) for MCS12. One-year mean change scores were -.4 for the PCS36 and -.6. for the PCS12. Mean change scores were +0.8 versus +1.1 for the MCS36 compared to the MCS12. Distributions of summary measures for both versions were comparable. At baseline, 25th, 50th and 75th percentiles of the PCS36, were 24.9, 32.4 and 43.4 respectively, compared to 25.8, 32.9, and 43.0 for PCS12. 25th, 50th and 75th percentiles of baseline MCS36 were 36.7, 49.4 and 57.5 respectively, compared to 37.2, 48.7 and 57.1 for MCS12. Distributions of 1-year change scores were also comparable.
Conclusions: Comparison of descriptive statistics for SF-36 versus SF-12 summary scores showed a high level of agreement. Estimates of percentile scores were highly congruent. Results suggest that normative and interpretive guidelines published for the SF-36 may be useful in interpreting SF-12 scores derived from large groups of VA primary care patients.
Impact statement: The SF-12 appears to be a reasonable alternative to the SF-36 for measuring general health status in large VA populations.