Comparison between two different measures of self-rated health: a single-question measure and a visual analogue scale.

INTRODUCTION: Self-rated health (SRH) is a useful concept for research and health planning, and an important indicator of population health. AIM: The present study aims to evaluate the appropriateness of two different measures used to assess SRH, a single question with a five-response Likert-type scale and a visual analogue scale (VAS), by studying the correlation between the two measures and the factors influencing response rates according to respondent characteristics. MATERIAL AND METHODS: A population-based postal survey was carried out within the framework of a World Health Organisation (WHO) project, with a national sample of randomly selected geographically stratified individuals. The factors influencing SRH using each measure were determined. The comparison of the two measures was also studied with respect to response frequencies and differences in association with potential determinants (age, sex, income, education). Answering to each measure depending upon answering to the other measure was also tested. RESULTS: The maximum correlation between the two measures was p = -0.78 (p < 0.001). Age, sex, income and education had an effect on SRH as measured using both measures. More people replies to the single question measure irrespective of any particular socio-economic characteristic. Generally, those completing the VAS were women of higher income. CONCLUSIONS: The two measures are moderately correlated, the structure of the questionnaire and sequence of questions seems to affect correlation, and the single question yields higher response rate than VAS does. Still, other factors may also play a significant explanatory role in SRH among the Greek population and in relation to which measure is used.