Familial correlations for serial measurements of recumbent length and stature.

Familial correlation coefficients were calculated for recumbent length or stature measured serially on participants in the Fels Longitudinal Growth Study and for short-term serial or cross-sectional measurements on relatives of participants. Pairs of relatives are compared at the same chronological ages from 1 to 18 years in 1-year increments and again in adulthood. First-degree relatives are more similar than second- or third-degree relatives at all ages. Sibling correlations are consistently higher than parent-offspring correlations, except after age 15, when they become very similar. For the most part, these results agree with those of cross-sectional studies finding higher sibling than parent-offspring correlations. Familial correlations tend to decrease during adolescence, perhaps due to differences among relatives in timing of growth spurts. Trends observed in bivariate plots of correlations over age are confirmed by multivariate analysis of correlations for different types of relatives at different ages. The largest amount of variation in familial correlations is due to the degree of relationship, although the amount of genetic similarity is difficult to separate from the effects of common family environment and generational differences. Age, sex and generation also play a role in multivariate prediction of the magnitude of familial correlations.