An assessment of the construct validity of the SF-12 summary scores acrossethnic groups

Background The aim of the study was to determine the construct validity of the 12-item Short Form health survey questionnaire (SF-12) across ethnic gr oups in a large community sample of the United Kingdom. Methods A postal survey was carried out in English using a questionnaire bo oklet, containing the SF-12 and a number of other items relating to experie nces of chronic illness and utilization of health care services. The datase t was the National Survey of NHS Patients. The sample consisted of 1000 res idents within each Health Authority in England who were randomly selected f rom the electoral registers, giving an initial sample of 100 000. Results A total of 61 426 (61.4 per cent) questionnaires were returned; 94. 3 per cent of respondents classified themselves as white and 5.7 per cent c lassified themselves as members of other ethnic groups. Construct validity of the SF-12 was assessed by comparing results from the two summary scores (the Mental Health Component Summary (MCS) score and the Physical Health Co mponent Summary (PCS) score) with overall self-assessed health and limiting longstanding illness. Although there were generally consistent patterns of association between overall self-assessed health or limiting longstanding illness and the MCS and PCS scores in all the ethnic groups, there were sig nificant differences between the MCS and PCS scores of Indians, Pakistanis and Bangladeshis who understood English fluently and those who did not. Fur thermore, there were differences in the completion rates of the SF-12 betwe en ethnic groups and a reversal of the general pattern of increasing MCS sc ores with increasing age in Bangladeshis. Conclusion The results indicate that the use of the SF-12 to measure the he alth of ethnic minorities seems acceptable in most instances, but may prove problematic in those instances where respondents complete the questionnair e via an untrained translator, such as a friend or family member. The syste matic differences in MCS and PCS scores between ethnic minorities who under stood English fluently and those who did not suggest that the meaning of sp ecific SF-12 items may change when informally translated. Future research u sing the SF-12 to measure the health status of ethnic minorities in the Uni ted Kingdom via postal surveys must include questions on whether respondent s completed the questionnaires via informal translations. In general, those wishing to measure the health of members of ethnic groups who are unable t o read English might consider using different techniques to gain the inform ation from these groups.