On each group of boys or girls in every school year of primary schools and junior high schools in Kyoto city, the joint distribution of height and weight was investigated based on the data in April 1976, and the distribution was compared with that in 1966.
The arithmetical means and standard deviations of height and weight, the correlation coefficient between height and weight, and the regression coefficient of weight on height were calculated (Table 1). Besides, the median, 10th and 90th percentiles of weight distribution in every group of height (1cm in width) were calculated to note the characteristics of the joint distribution more clearly (Fig. 1, Fig. 2, Table 2).
In every group of boys or girls in every school year, the arithmetical means of height and weight, and the standard deviation of weigth in 1976 were greater than those in 1966. But the differences between 1976 and 1966 were negligible as for the correlation between height and weight, and the regression coefficient of weight on height.
For boys in the school year from the second to sixth in the primary school, and for girls in the school year from the third to sixth in the primary school and in the first school year of the junior high school, the median, 10th and 90th percentiles of weight corresponding to the same height were almost the same in 1976 and in 1966, for every group of height.
For boys in the first school year of the primary school and for girls in the first and second school year of the primary school and in the third school year of the junior high school, 90th percentile of weight corresponding to the same height was greater in 1976 for relatively tall children. For boys in every school year of the junior high school, 90th percentile of weight corresponding to the same height was greater in 1976 for every group of height. However, for these groups of school children, the median and 10th percentile of weight corresponding to the same height were almost the same in both years.
For girls in the second grade school year of the junior high school, the median and 90th percentile of weight corresponding to the same height were greater in 1976 for relatively short children. The difference of the form of the joint distribution between 1976 and 1966 seemed to suggest the acceleration of growth since 1966.
