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.