PRINCIPAL COMPONENTS-ANALYSIS OF MORPHOLOGICAL MEASURES IN THE QUEBECFAMILY STUDY - FAMILIAR CORRELATIONS

Principal components analysis was carried out on 13 morphological dime nsions collected in the first phase of the Quebec Family Study (weight , height, fat mass (FM), fat-free mass (FFM), body surface area, six s kinfolds, arm and calf girths). The first four principal components (P Cs) account for 85.9% of the total phenotypic variance in the anthropo metric dimensions. The first PC has almost equal loadings on the 13 va riables, indicating its role as an overall body size and adiposity mea sure. This interpretation is supported by its high intraindividual cor relations with other composite indices such as the BMI and sum of six skinfolds (SF6). An interesting finding compared to other studies deal ing with PCs of only skinfolds is that the second component appears to contrast measures of body fat with those that are fat free or that re present overall body size, thus indexing a different dimension to the fat patterning. It explains 17% of the total phenotypic variance. The commonly observed component for the trunk-extremity contrast is repres ented as the fourth principal component. The third component primarily indexes height, although an extremity-trunk contrast is also weakly r epresented. Together, the 3rd and 4th components explain similar to 10 % of the total variance. The intraindividual correlation of PC3 with t he trunk-extremity skinfold ratio (TER) is moderately negative (-0.307 ), whereas that of PC4 is highly positive (0.764). Analysis of familia l correlations (parent-offspring and sibling) shows that the familial effect (transmissibility) ranges 0.43-0.75 for the first four PCs. The lack of significant spouse correlation for most of the PCs suggests t hat these familial effects may be primarily genetic. (C) 1997 Wiley-Li ss, Inc.