The human sex ratio and factors influencing family size in Japan.

In 1979 sex data were obtained from 861 Japanese students from three upper secondary school (Katsushikano, Ogikubo, and Kiyose) located in the residential, metropolitan area of Japan. Average numbers of children per family were 5.16 for the parental and 2.43 for the present generation. Secondary sex ratios were 106.9 and 104.9 for the parental and present generation, respectively. Neither the similarity or dissimilarity of sexes nor the proportion of males in existing children was significantly associated with family size in the present generation. A significant positive correlation was found between sexes of child 1 and 2 in families of two or more children. None of the other correlations between successive births or between nonsuccessive births was significant. Observed frequencies of combinations of sexes within families of the parental and present generations did not differ from expected frequencies. The family most preferred by both male and female respondents consisted of two children representing both sexes with the first-born being male. The desired families were characterized by an average of 2.35 children and a resulting sex ratio of 122 males: 100 females.