Cancer rates should not be adjusted for socio-economic status in international comparisons

A new paper, published in the Journal of Cancer Epidemiology, by researchers at the Northern Ireland Cancer Registry and National Cancer Registry (including Prof Linda Sharp, Dr Sandra Deady, Mr Neil McCluskey and Dr Harry Comber), reports that cancer rates should not be adjusted for socio-economic status when making international comparisons.

Cancer incidence rates vary between countries, even after adjustment for difference in age distributions. Rates also vary within countries by socio-economic status, suggesting that some of the international variation may be due to between-country differences in socio-economic circumstances.

Using data from the two registries in Ireland, the research team investigated the effect of adjusting for socio-economic status on comparisons of cancer rates between Northern Ireland and the Republic of Ireland. For those cancers which are strongly related to socio-economic status – such as lung and cervical cancer - this adjustment had a major impact on the international comparison. In some instances, the adjustment for socio-economic status attenuated international differences, while in others it accentuated them. For cancers that are weakly associated with socio-economic status, the adjustment had little impact on international comparisons.

The authors conclude that socioeconomic factors explain some international variations but also obscure other crucial differences; thus, adjustment for these factors should not become part of international comparisons.