Socio-economic inequalities in mortality. Methodological problems illustrated with three examples from Europe

Background: Studies from most European countries have been able to demonstr ate that lower socioeconomic groups have higher risks of disease, disabilit y and premature death. Uncertain is, however, whether these studies have al so been able to estimate the precise magnitude of these inequalities, their patterns and their trends over time. The purpose of this paper is to illus trate the extent to which results of descriptive studies can be biased due to problems with the data that are commonly available to European countries . Methods: Three illustrations are presented from a project on socio-economic inequalities in premature morbidity and mortality in Europe. These illustr ations concern three problems often encountered in data on social class dif ferences in mortality among middle aged men: the numerator/denominator bias in cross-sectional studies (illustrated for France), the exclusion of econ omically inactive men (illustrated for 4 countries), and the use of approxi mate social class schemes (illustrated for Sweden). Results: In each illustration, inequalities in mortality among middle aged men could be demonstrated, but data problems appeared to bias estimates of the precise magnitude of inequalities in mortality, their patterns by socia l class and cause of death, and their trends over time. The bins was substa ntial in most cases. Usually, it was difficult to predict in which ways and to what extent inequality estimates would have been biased. Conclusions: When the aim of a study is to determine the precise magnitude, patterns or time trends of health inequalities, the results should be eval uated carefully against a number of potential data problems. Investments ar e needed, e.g. in data sources and in the measurement of socio-economic sta tus, to secure that future studies can describe socio-economic inequalities in health in Europe in more detail and with more reliability.