EVIDENCE FOR THE SENSITIVITY OF THE SF-36 HEALTH-STATUS MEASURE TO INEQUALITIES IN HEALTH - RESULTS FROM THE OXFORD HEALTHY LIFE-STYLES SURVEY

Objectives - The short form 36 (SF-36) health questionnaire may not be appropriate for population surveys assessing health gain because of t he low responsiveness (sensitivity to change) of domains on the measur e. An hypothesised health gain of respondents in social class V to tha t of those in social class I indicated only marginal improvement in se lf reported health. Subgroup analysis, however, showed that the SF-36 would indicate dramatic changes if the health of social class V could be improved to that of social class I. Design - Postal survey using a questionnaire booklet containing the SF-36 and a number of other items concerned with lifestyles and illness. A letter outlining the purpose of the study was included. Setting - The sample was drawn from family health services authority (FHSA) computerised registers for Berkshire , Buckinghamshire, Northamptonshire, and Oxfordshire. Sample - The que stionnaire was sent to 13 042 randomly selected subjects between the a ges of 17-65. Altogether 9332 (72%) responded. Outcome measures - Scor es for the eight dimensions of the SF-36. Statistics - The sensitivity of the SF-36 was tested by hypothesising that the scores of those in the bottom quartile of the SF-36 scores in class V could be improved t o the level of the scores from the bottom quartile of SF-36 scores in class I using the effect size statistic. Results - SF-36 scores for th e population at the 25th, 50th, and 75th centiles were provided. Those who reported worse health on each dimension of the SF-36 (ie in the l owest 25% of scores) differ dramatically between social class I and V. Large effect sizes were gained on all but one dimension of the SF-36 when the health of those in the bottom quartile of the SF-36 scores in class V were hypothesised to have improved to the level of the scores from the bottom quartile of SF-36 scores in class P. Conclusions - An alysis of SF-36 data at a population level is inappropriate; subgroup analysis is more appropriate. The data suggest that if it were possibl e to improve the functioning and wellbeing of those in worst health in class V to those reporting the worst health in class I the improvemen t would be dramatic. Furthermore, differences between the classes dete cted by the SF-36 are substantial and more dramatic than might previou sly have been imagined.