Abstract
The discipline of epidemiology includes the study of patterns of disease and the association of disease with demographic, biological, sociological, and behavioural characteristics in a population. Within the discipline there are several distinct research designs which can be applied to determine the nature and extent of disease, to develop hypotheses about causation, and to test such hypotheses through experimentation. Some of the correlates of ill health are not, however, readily amenable to experimental or intervention study. Behind those factors contributing to the causation of disease on the one hand, and the prevention of disease and the promotion of health on the other, are a number of complex determinants which include socio-economic status and the factors contributing to that state, social influences on behaviour of particular groups within society, and personal and family beliefs about self-image and control over one's health'. These are factors which bear directly on life-style or life events, or affect the social structure of a community or nation, and are thus difficult to manipulate experimentally. In such circumstances, the cohort study can be of particular value for studying the influence of these variables on the prevalence and incidence of a wide variety of parameters. By following a group of subjects over a long period, it is possible to study the subjects in considerable depth, to examine associations, and to test hypotheses in a prospective manner. Cohort studies involving dental health are not common. Even more uncommon in dentistry are cohort studies of a multidisciplinary nature in which data from a variety of sources can be applied to problems in dental health or dental care. The Nymegen Growth Study, in which the dental input has been largely but not exclusively centred on craniofacial growth and orthodontic considerations, is a notable example of dental involvement in multidisciplinary longitudinal research. The Dunedin Multidisciplinary Health and Development Study is a further research programme in which dental health has been integrated with an extensive range of investigations of a large cohort.