Criterion validity and reliability of the SF-36 in a population sample

This study aimed to determine the criterion validity of the Short Form 36 health survey questionnaire (SF-36) in a large community sample, and to explore the instrument's internal consistency and validity in groups reporting different levels of ill-health. A postal survey was undertaken using a questionnaire booklet, containing the SF-36 and a number of other items concerned with lifestyles and illness. The questionnaire booklet was sent to 13 042 randomly selected subjects between the ages of 18–64 years, drawn from Family Health Services Authority (FHSA) computerized registers for Berkshire, Buckinghamshire, Northamptonshire and Oxfordshire. This paper is based upon the 9332 (72%) responses gained. Scores for the functional status and well-being scales of the SF-36 were used as outcome measures. The response rate for the questionnaire booklet was 72%. Internal consistency of domains was found to be high, both for the sample as a whole, and when broken down by specific subgroups. Criterion validity was assessed by comparing scores for the seven multi-item dimensions assessing functional status and well being with a single global health question. The global question was the first item of the SF-36 and asks respondents to evaluate their health ‘overall’. Statistically significant trends were observed for decreasing SF-36 scores (i.e., those indicating greater health problems) with worsening self-rated general health. These results provide further psychometric evidence for the use of the SF-36 when used with groups reporting varying extents of ill-health.