Season of Birth and Mental Deficiency

Abstract

The births of 10,705 mentally deficient subjects (6106 males and 4599 females) born during the years from 1911 through 1958 were studied as to their distribution over various months of the year. Statistics revealed that they were born significantly less often in Sept. than control subjects. This proved to be mainly due to subjects with Down''s syndrome (mongolism) having fewer birthdays in Sept. than in the other months. The validity of any conclusions drawn from these statistics was discussed. An analysis of different groups within the Swedish population, at different times, revealed that many circumstances affect the shape of the annual birth curve. Because of the impossibility of getting a satisfactory control series from official statistics, it was concluded to any report that a certain group differed from the normal in season of birth with scepticism.