Income distribution and mortality: Implications from a comparison of individual-level analysis and multilevel analysis with Swedish data

Background: This follow-up study analyses whether there is an association between income distribution in Swedish municipalities and risk of death from all causes in the total Swedish population aged 40-64 years and compares the results obtained with analyses performed on individual-level analysis and multilevel analysis. Methods: Individual-level data on social and economic circumstances were obtained from various official records and were linked to the national cause-of-death register. Analyses were made with two methods, an individual-level regression and a multilevel regression. The study population comprised all people 40-64 years of age in the 1990 Swedish census, altogether 2.57 million people in 284 municipalities. Results: The main results showed that in the individual-level regression the income distribution showed a positive and significant association ( risk ratio = 1.29; 95% CI = 1.24-1.34) with higher mortality for those living in municipalities with higher income inequality. This association was not found in the multilevel regression analysis ( RR = 1.03; 95% CI = 0.94-1.13). Conclusion: There seems to be no association between income distribution and mortality in Sweden when considering the possibility of clustering in municipalities. Further studies on the relationship between income inequality and health should aim at elucidate processes within area-level units.