Epidemiological surveys of senile dementia in Japan.

Epidemiological surveys of senile dementia at home were carried out on 3,754 subjects for two consecutive years, 1987 and 1988. The prevalence and incidence rates were 4.1% and 1.01%, respectively. Concerning the incidence rate, the sample populations of previous reports were small in number--less than 1,000. If we suppose that the incidence were to be approximately 1%, then it follows that dementia would be noted yearly in no more than one out of 100 senile subjects. A difference in subject number leads to a great difference in the incidence. Therefore, it is necessary that the number of subjects should be more than 1,000 for a comprehensive epidemiological survey of incidence rate of senile dementia. Accordingly, the present study is a better representation of the true picture as it was obtained by a more accurate method accompanied by less errors.