Prospective Urban Rural Epidemiology (PURE) study: Baseline characteristics of the household sample and comparative analyses with national data in 17 countries

Background The PURE study was established to investigate associations between social, behavioural, genetic, and environmental factors and cardiovascular diseases in 17 countries. In this analysis we compare the age, sex, urban/rural, mortality, and educational profiles of the PURE participants to national statistics. Methods PURE employed a community-based sampling and recruitment strategy where urban and rural communities were selected within countries. Within communities, representative samples of adults aged 35 to 70 years and their household members (n = 424,921) were invited for participation. Results The PURE household population compared to national statistics had more women (sex ratio 95.1 men per 100 women vs 100.3) and was older (33.1 years vs 27.3), although age had a positive linear relationship between the two data sources (Pearson's r = 0.92). PURE was 59.3% urban compared to an average of 63.1% in participating countries. The distribution of education was less than 7% different for each category, although PURE households typically had higher levels of education. For example, 37.8% of PURE household members had completed secondary education compared to 31.3% in the national data. Age-adjusted annual mortality rates showed positive correlation for men (r = 0.91) and women (r = 0.92) but were lower in PURE compared to national statistics (7.9 per 1000 vs 8.7 for men; 6.7 vs 8.1 for women). Conclusions These findings indicate that modest differences exist between the PURE household population and national data for the indicators studied. These differences, however, are unlikely to have much influence on exposure-disease associations derived in PURE. Further, incidence estimates from PURE, stratified according to sex and/or urban/rural location will enable valid comparisons of the relative rates of various cardiovascular outcomes across countries.