Proxy reporting and the increasing prevalence of arthritis in Canada

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Background Analyses of the 1994/95 to 1998/99 Canadian National Population Health Surveys (NPHS) reveal significant, and greater than projected, increases in the reported arthritis in the household population aged 15+ years, from 13.4 to 16.0%. The objectives of this study were to determine whether the increasing prevalence of arthritis can be explained by a) changes in the age and sex structure of the population, or b) the variation in the proportion of proxy respondents and whether proxy reporting affects the overall prevalence estimate. Methods Overall analyses of 1994/95, 1996/97 and 1998/99 cycles of the NPHS, for arthritis or rheumatism reported as a long-term health problem diagnosed by a health professional. Stratified analyses, by respondent type, to account for the decreasing proportion of proxy respondents over time (33% to 16%). Results Overall age-sex standardized prevalence estimates were similar to crude estimates. The crude prevalence of arthritis in proxy respondents was stable (approximately 8.5%), whereas in self-respondents it increased from 15.8 to 17.4% over the 3 cycles. Adjustment for the lower prevalence in proxy respondents increased the estimated overall prevalence of arthritis by at least 1 percentage point for each cycle year. The disparity between self- and proxy reporting was higher for younger people and females. Conclusion Significant disparity exists in age- and sex-specific prevalence estimates between self- and proxy respondents. The increase in prevalence of arthritis over time is a result of increased reporting by self-respondents. Proxy reporting affects overall prevalence. The findings have implications for the use of NPHS data.