Epidemiological features of first-visit outpatients in Japan: comparison with general population and variation by sex, age, and season.

To evaluate the methodological issues in using first-visit outpatients as controls in epidemiological studies, the features of general lifestyles of non-cancer outpatients at Aichi Cancer Center Hospital (ACCH) were compared with those of the general population, and their variation by sex, age, and season was determined by using a self-administered questionnaire. The study included 1231 subjects randomly selected from the Nagoya electoral roll (CRG), and three groups of non-cancer ACCH outpatients living in Nagoya; 800 from the period September to December 1992 (OPG1), 2326 from January to December 1992 (OPG2), and 12,243 from January 1991 to December 1992 (OPG3). In the younger age group, the proportion of current smokers was higher in the CRG than in the OPGs. In the older age groups, the proportion of those who consumed fresh vegetables and fruit everyday was higher in the OPGs than in the CRG. For other items, the features of the OPGs were not significantly different from those of the CRG. Among the OPG3, there were differences in the features of general lifestyles between sexes and consumption of several food items varied with age. Seasonal variation, however, was only observed in the specific food items where supply varied seasonally. It was concluded that, with due consideration of age, sex, and season in the analysis, it is feasible to use non-cancer outpatients as controls in epidemiological studies.