Age in epidemiological analysis
- TNO Prevention and Health, PO Box 2215, 2301 CE Leiden, Netherlands
- Correspondence to: Dr S A Reijneveld; sa.reijneveld{at}pg.tno.nl
It still merits attention
Analyses by age are among the most widely used tools from the epidemiological toolbox. They are mostly used to adjust for confounding (as a result of age) or to assess effect modification. The epidemiologist generally handles age in two ways: as a continuous variable, or as a categorised variable by combining a number of adjacent ages into a joint category. When looking at age as a continuous variable, standard epidemiological textbooks such as Rothman and Greenland’s and many others recommend registering age as precisely as possible.1 They also draw attention to the handling of age, especially to the way in which categories are chosen. Categories should not be too extensive to prevent residual confounding by age (an incomplete adjustment for age as the variation of a risk within a category is too wide).1 To stimulate comparisons of studies, the International Journal of Epidemiology even provides guidelines on forming categories: …
