International comparisons in measuring health states: experiences from the world health surveys

During the last three decades, there has been general acceptance of an approach to describing health states of individuals in terms of multiple domains of health, and in developing self-report instruments that seek information on each of these domains. A health state is thus a multi-dimensional attribute of an individual that reflects his or her levels on the various components or domains of health. Thus, a health state differs from pathology, risk factors or etiology, and from health service encounters or interventions.

How to describe health states, is a central challenge in undertaking the measurement of health. The relationship of health states to other aspects of health such as future non-fatal health outcomes or risk of mortality need to be examined. The way people report their own health varies consistently with factors such as education, sex, age, or other cultural factors. Various people use different response category cut-points across cultures or population sub-groups, and this 'response shift' implies that self-report categorical data are not comparable across individuals. The responses cannot be directly used to measure health without adjustment.

In recognition of this the WHO World Health Surveys (WHS), used a set of questions across a core set of domains to measure health states and employed vignettes to detect and correct for biases in self-report in order to adjust for response category cut-point shifts. This paper will describe the instrument used in the WHS and the methods used to provide cross population comparable data. It will present results from the WHS demonstrating the existence of systematic reporting biases, the ability of respondents to rate vignettes and their use to adjust for biases in order to make data more comparable. Future strategies to address these problems will be discussed.