Résumé :
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[BDSP. Notice produite par INIST-CNRS R0xnbiqP. Diffusion soumise à autorisation]. Background : Individuals of lower socio-economic status (SES) are less likely to participate in health surveys than individuals of a higher SES. It is, however, not known whether this difference in participation is associated with health status. This study sets out to assess whether a population health survey gives biased estimates of socio-economic inequalities in self-reported health. Methods : We compared two independent cross-national data collections, a national health interview survey (n=10164) and a census (n=8 491 528), both carried out in Belgium in 2001 and posing the same health question. We computed the prevalence ratios of poor subjective health among socio-economic groups. To estimate the bias, a relative odds ratio (ROR) was computed as the ratio of the survey prevalence ratio to the census prevalence ratio. Results : Less-educated individuals had a lower risk of poor health status in the survey [Prevalence ratio=1.66,95% confidence interval (CI) : 1.48-1.86] than in the census (Prevalence ratio=2.23) leading to an underestimation of the risk associated with low education (ROR=0.74,95% CI 0.66-0.83). Compared with better-off groups, those who were not working or who were less educated were generally less likely to participate in the survey when they had a poor health status. Conclusions : Overall, the health survey underestimated the effects of low SES on poor health status, due to selection bias. We conclude that strategies to improve participation among disadvantaged socio-economic groups should be identified.
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