Time-series analysis of stature and body weight in five siblings

Since 1971, stature and body weight in five siblings have been measured monthly. Time-series analysis of stature, body weight and their increments per month was made by the Program of Census Method IIX11 resulting in three components: a trend-and-cycle factor, a seasonal factor and an irregular factor. Significant seasonal variation was found in both stature and body weight. In two young subjects, trend curves of stature are very close to each other while those of body weight are different. Trend factor in increment indicates that growth rate of stature or body weight fluctuates, instead of being smooth, suggesting that from birth to maturity acceleration and deceleration occur alternately, like repeated retardations and subsequent catch-ups. A high peak of body weight increment precedes menarche by 1 1/2 years in two girls. In one case, no adolescent spurt in stature was observed while a high peak appeared in body weight in that period. Irregularity in stature is about one-tenth that of body weight when the two are compared in terms of the ratio of SD of irregular factor/mean of trend factor. The raw data are given in an appendix.