The WHO Meeting of Investigators on Methodology of Twin Studies was held in Geneva from 24 October to 1 November 1965. The meeting was opened by Dr L. Verhoestraete, Director, Division of Health Protection and Promotion, who welcomed the participants. He said that this meeting of geneticists, epidemiologists and clinicians had been called to review the possible contribution of twin studies, a recognized tool in genetic research, to the broader field of epidemiological investigations, where so far they had found comparatively little use.

Professor D. D. Reid was elected Chairman; Professor L. Gedda, Vice-Chairman and Dr R. Cederlöf, Rapporteur.

Studies of general population characteristics include vital statistics such as mortality and morbidity data which are obtained on a routine basis. These data constitute one of the best sources of raw material for epidemiological studies and provide easily accessible information for basic research and for programme planning in control of disease. Very often they raise questions concerning the epidemiology of chronic disease, which may help delineate the relevant factors and provide guiding hypotheses for further research in this field. A deeper understanding of disease may also be arrived at through the study of individual characteristics in cross-sectional, retrospective and prospective studies, and through experimental investigations. A cross-sectional study can be used not only in determining prevalence of disease in a population, but it can also serve as the base-point for a longitudinal study of chronic diseases.