Problem with cancer (and all diseases) is that it happens anyway, and clusters of cases do happen naturally. Suppose an area had below-average figures for a few years, then suddenly had lots in one year. Is there something causing them, or is it just a high-point in the average? And it's always easier to find someone or something to blame than it is to say that it's just seriously bad luck, so anything around which is slightly out of the ordinary could be picked on as a culprit. OTOH, there may be cases (eg. dioxin pollution) where there genuinely is a danger and it gets passed by. That's where epidemiologists earn their money.

Grab.