This century has seen remarkable growth in the scale and power of the studies carried out by epidemiologists, and in the sophistication and skill with which those studies have been conducted. The growth of the science has been driven by the increased incidence of cancer and the pressure from governments and citizens to have answers, and has been greatly enhanced by the increasing availability of computers and the application of information technology to collecting the facts about cancer in the population.

Epidemiology proceeds on a broad front, integrating knowledge from cancer registries (collections of statistics on officially reported cancer occurrence and mortality), clinical studies and specific studies designed to answer a single question about a possible link between a cancer and a possible causative factor. Answers can often only be deduced by adding together all of these approaches. However, it is easier to describe how epidemiologists work by splitting their activities rather artificially into two kinds: descriptive work and analytical work.

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Cancer