Background: An increase has been observed in differences in mortality between the richest and poorest areas of rich countries. This study assesses whether one of the proposed explanations, i.e., population change, might be responsible for this increase in Spain.
Methods: Observational study based on average income, population change and mortality at provincial level. The premature mortality rate (ages 0-74 years) was estimated for all causes and for cancer, cardiovascular disease and external causes across the period 1980-2010. In the years analysed, provinces were grouped into tertiles based on provincial income, with the mortality rate ratio (MMR) being estimated by taking the tertile of highest-income provinces as reference. Population change was then controlled for to ascertain whether it would modify the rate ratio.
Results: In all-cause mortality, the magnitude of the MRR for provinces in the poorest versus the richest tertile was 1.01 in 1980 and 1.12 in 2010; in cardiovascular mortality, the MMRs for these same years were 1.08 and 1.31 respectively; and in the case of cancer and external-cause mortality, MMR magnitude was similar in 1980 and 2010. The magnitude of the MMR remained unchanged in response to adjustment for population change, with the single exception of 1980, when it increased in all-cause and cardiovascular mortality.
Conclusion: The increase in the difference in premature mortality between the richest and poorest areas in Spain is due to the increased difference in cardiovascular mortality. This increase is not accounted for by population change. In rich countries, more empirical evidence is thus needed to test other alternative explanations for the increase in economic differences in mortality.