Controlling for socioeconomic disadvantage in epidemiologic analyses.

Controlling for the effects of socioeconomic disadvantage is commonplace in epidemiologic studies. In New Zealand, the Elley Irving scale is used to classify individuals into socioeconomic groups. In this study, data from the control group of a large population based case-control study were used to examine the extent to which indicators of socioeconomic disadvantage vary between ethnic groups, within socioeconomic strata. In each of the commonly constructed socioeconomic strata, the proportion of subjects with car access was significantly lower in the Maori/Pacific Island group than in the nonMaori/Pacific Island group. Similarly, apart from in the highest socioeconomic stratum, where the numbers in the Maori/Pacific Island group were small, the proportion of subjects who were owner occupiers was significantly lower in the Maori/Pacific Island group compared with the nonMaori/Pacific Island group, in each stratum. The Elley Irving scale has limited utility as a measure of material well being. Its widespread use in epidemiologic research, to control for the effects of socioeconomic disadvantage must therefore be questioned.