| Abstract: | In a stable, economically- and educationally-privileged population of 180 subjects observed from birth to beyond the period of maximum growth in height, no secular changes toward larger size or earlier adolescence were observed between the earlier-born and later-born boys or girls of the Child Research Council study series. The mid-birthdate for the 45 years of data collection was January 1, 1940 for the girls and May 1, 1936 for the boys. With none of the mean differences significant at the 0.05 level of confidence, the earlier-born subjects were both slightly taller and heavier from birth and, for the girls, adolescence was slightly earlier. Forty pairs of like-sexed siblings were included in the data. Coefficients of correlation were statistically significant for birthweight and menarcheal ages for the sisters and for height and weight at the age of maximum increment of growth in height for both sexes. In 12 of the 16 pairs of sisters, the older menstruated at an earlier age than the younger. |
