Abstract

Epidemiology is based on a very simple principle: diseases do not occur at random, but in patterns that reflect their causes. The corollary is that by studying patterns of disease, it is possible to identify the causes of those diseases. And for many types of disease the application of this principle has been outstandingly successful. As Stolley and Lasky pointed out in their excellent and readable book, Investigating Disease Patterns (Stolley & Laskey 1998), it is not an exaggeration to say that much of what we know about the causes of cancer, of infectious disease and of chronic conditions such as coronary heart disease is derived from epidemiological studies. Epidemiology has also identified many environmental influences that cause illness. The dangers of cigarette smoking, exposure to mineral dusts, ionizing radiation, lead and a host of other substances present in the environment have been discovered and quantified largely through epidemiological investigations.