Studies of the human sex ratio and factors influencing family size in Botucatu, Brazil.

During 1974--75, data on sex and family size were obtained from approximately 500 Brazilian college students and their parents. Sex ratios for the immediate and parental generations were 107:100 and 106:100, respectively. Correlation coefficients were calculated between sexes of various children in families of the immediate generation. A significant positive relationship was found between sexes of the first two children in families of two or more children. The overall correlation between sexes of successive births was positive but not significant. Correlation coefficients between sexes separated by one or more births were not significant. The observed frequencies of combinations of sexes within the various family sizes did not differ from expected frequencies. Average numbers of children per family were 4.39 and 6.80 for the immediate and parental generations, respectively. Average family sizes decreased as the formal educational level of the parents increased. If the parents' desired both sexes of children, such preferences had no measurable influence on family size.