Are socioeconomic inequalities in mortality decreasing or increasing within some British regions? An observational study, 1990-1998.

BACKGROUND: This paper evaluates claims in a recent study that inequalities in small area mortality rates have lessened. We examine the effect of differently estimated populations on time trends in age-specific mortality rates for Yorkshire and the Humber and East of England.
METHODS: Populations were estimated for wards using four methods that introduce increasing amounts of information. Age-specific mortality rates for age-groups 45-54, 55-64, 65-74 and 75-84 for both sexes were calculated for population-weighted deprivation quintiles. Inequality was tracked using ratios of rates in the most deprived quintile divided bythose in the least.
RESULTS: When constant 1991 populations are used, rate ratios decrease for all age-sex groups, indicating shrinking inequality. When a method adjusting small area populations to official district estimates is used, both decreases and increases are observed in the mortality rate ratios. These results differ from Trent region findings of decreases in inequality. When small area populations are cohort-survived and adjusted to district populations, most differences in rate ratios indicate increasing inequality. When a method is used that includes information on migration and special populations, then seven out of eight age-sex groups exhibit increasing inequality.
CONCLUSIONS: A judgement about trends in mortality inequality is highly dependent upon the denominator population used. Simpler estimation methods result in convergence of rate ratios, whereas more sophisticated methods result in increasing inequalities in most age-sex groups.