Profile comparisons of physical growth for monozygotic and dizygotic twin pairs

Abstract

Three different methods of analyzing similarity of physical growth curves within MZ [monozygotic] and DZ [dizygotic] twin pairs are compared. The concordance of the curves for each pair can be measured by either a multiple regression coefficient (R2) or the square root of the sum of squared differences between corresponding deviation points (D). The latter seems to be a more appropriate measure of profile contour similarity, mainly because the distance between curves is allowed for. An intra-class correlation based on a longitudinal analysis of variance seems to be a useful measure of average profile similarity for comparing groups of individuals. The distributions of the D measures, calculated for all MZ and DZ twin pairs , show MZ pairs to have significantly smaller D-values for both height and weight, on average, than DZ pairs. The intra-class correlations also show a higher concordance in developmental profile for MZ in comparison to DZ.