Growth curve and age of maximum increment in the mean height for Koreans

Abstract

The Annual Report of Statistics on Education, published yearly by the Korean Government, provides data on the mean height of Korean children at ages 6-17 from 1962 to 1983. By converting the annual cross-sectional data into birth-year cohorts to obtain the growth curve and annual height increments at each cohort, an attempt was made to clarify the recent acceleration of growth among Korean children. The results were as follows: 1) The 1967 cohort of boys, i.e. boys born in 1967, indicated that the age of maximum increment in mean height (MI age) was 13.21 years of age and the 1970 cohort of girls was 10.50 years of age. Their adolescent growth levels were almost the same as the levels for Japanese born in the same period. 2) The 1949-1962 cohorts of both sexes indicated that annual height increments had two modes at 12 and 15 years of age, i.e. bimodality. The ages corresponding to these two modes fall on the points immediately after going on to junior or senior high school, and there were statistically negative correla- tions between annual increments at these ages and the ratio of students going on to high schools. 3) In the cohorts in which the said ratio was relatively lower, those who entered the upper schools were inclined to be superior to non-high school students in height. It is, therefore, considered that the specific bimodality of annual height increments resulted from the said tendancy, that is, from abnormally large increments due to the quality of population size. 4) Our method of calculation computed out the MI age of the cohorts (for boys born in 1965, girls in 1966 and after) showing unimodality. On the other hand, the MI age of the cohorts which showed bimodality was worked out from the estimated value on which the height growth after junior higt school in Korea was presumed by actually observing height growth for the whole six years of primary school. It was assumed that the height growth of Koreans follows almost the same growth curve as that of Japanese. The annual change of MI age was found to be in agreement with the logistic curve and a striking lowering.5) The acceleration of growth in Korea indicated a delay of 20-21 years when compared with Japan, and an acceleration rate was 1.3-1.4 times faster than Japan.