Evidence of age-related responses to short-term environmental variation: time series analysis of cross-sectional data from Taiwan, 1969 to 1990.

Abstract

Cross-sectional heights and weights collected by Taiwan's Ministry of Education since 1964, and reported separately for Taipei and rural townships from 1969 through 1990, were used to test the hypothesis that in Taiwan the degree to which increments of change in height and weight of urban or rural boys and girls tracked each other from year to year was a function of sex and age-related capacities to respond to common environmental forces. Five testable implications follow from this hypothesis. Results were evaluated using detrended time series derived correlations of yearly or near yearly change in sex-specific age group height or weight means within and across regions, cross-sectionally estimated ages of maximum change of height and weight, and evidence of response to two recessions. The hypothesis was largely supported by the available evidence. The similarities in secular change from year to year, with only a few exceptions, suggested that socioeconomic trends indirectly affected the pace of growth of children in both urban and rural Taiwan measured in the spring of the following year. The strength and age-related pattern of these correlations were consistent with sex and age-related capacities to respond to shared environmental factors. Evidence of lags between height and weight, found both in cross-sectionally estimated mean ages of maximum change in height and weight and in the pattern of within sex correlations also argued for the hypothesis. The evidence further suggested that when the economy faltered briefly in Taiwan following worldwide oil crises, children's growth was rapidly affected in an age-dependent manner. This study bolsters the view that secular changes in growth reflect environmental quality. It suggests as well that under some circumstances, environmental change may be rapidly reflected as mean changes in height or weight of certain age groups. The intensity of the response appears to be related to the degree of improvement or deprivation, the maturationally mediated pace of growth, and probably initial energy balance.