Although lacking the control available to toxicity studies, epidemiology allows for much larger study sizes and is particularly useful for identifying causal factors for population-wide health concerns. Some epidemiological studies are given more credence than their toxicological counterparts because the data are seen as more accurate for ‘real-life’ situations. Also, data collected for completely different reasons can often be incorporated into an epidemiological study. The greatest difference between epidemiology and toxicology, aside from the observational/experimental basis, is the measure of exposure, which, although it would improve any study, is often difficult to incorporate into epidemiological studies because of the historical nature of exposures.