Monitoring the self-reported health status of populations is an important input to health policy. Instruments commonly used to measure health status such as the SF-36 and its variants, the HUI III and the EQ-5D, do not capture all important domains of physiological and psychological functioning. A more comprehensive instrument was developed by the World Health Organization (WHO) for use in the 2001 Multi-country Survey, but was never used in its long form.
A modified version of this instrument, the WHO Long Form (New Zealand version), comprising 62 items in 14 scales, was included in the 2002/03 New Zealand Health Survey, a nationally representative household survey involving face-to-face interviews of 12,929 adults. The New Zealand adaptations included minor item changes in order to fully embed the SF-36, which was used in previous New Zealand health surveys.
The instrument was found to have excellent acceptability. Likert scaling assumptions were met for all items. Internal consistency (Cronbach’s alpha) exceeded 0.7 for all scales, indicating adequate reliability. The scale cross-correlation matrix indicated adequate construct validity. Discriminative validity, assessed by comparing mean scale scores of respondents with and without self-reported chronic disease, indicated adequate scale responsiveness for population health monitoring purposes.
Norms were successfully derived for all major population subgroups and showed the expected patterns, with males scoring higher than females on several scales, younger age groups scoring higher than older age groups on scales tapping physical but not mental health constructs, and variations in scale scores between ethnic groups that largely (but not entirely) mirrored objectively measured health inequalities.
We conclude that the WHO Long Form health status instrument (New Zealand version), modified as suggested in this report, is suitable for use when a comprehensive measure of self-reported health status is required in the context of population health monitoring. Ceiling effects, and response category cut-point shifting (as with all self-report instruments), are limitations users should be aware of, in addition to the respondent burden imposed by the use of a long form instrument.