General principles of epidemiology, as applied to studies of IgE-mediated food allergy.

Epidemiology is the study of the distribution of disease and of the factors which contribute to or determine the development of a disease. Descriptive studies measure the frequency of a disease whereas analytic studies are predominantly concerned with identifying determinants or causes. In any epidemiological study it is essential that the exact objectives are clearly understood in terms of definitions and diagnostic criteria for the condition under scrutiny. Rather than address all food-induced reactions and diseases, the issues raised by epidemiological studies of one main group of conditions with a common mechanism, IgE-mediated food allergy, are considered. Problems with population-based and hospital-based surveys include case definition, case ascertainment, calculations and presentation of results and small numbers with wide confidence limits.