Prediction of body density in young and middle-aged men

The purpose of this investigation was to predict body density of young (18-22 yr) and middle-aged (40-55 yr) men and to determine if generalized equations were appropriate to both populations. The dependent variable, body density, was determined by the hydrostatic technique. Independent variables included 7 skinfold fat, 11 girth, and 7 diameter measures; age; height; and weight. Mean body density for young men was 1.068 g/ml (SD +/- 0.014) and percent fat, 13.4 (SD +/- 6.0); the values for middle-aged subjects were 1.043 g/ml (SD +/- 0.0130) and 24.7% (SD +/- 5.9). Incomplete principal components analysis was used to examine the dimensions measured by the independent variables, and these analyses revealed differences between samples. Using multiple regression analysis, with the exception of girth measurements, the slopes of the regression lines were equal. For all analyses, however, the intercepts were different. These results confirmed the need for different regression equations for these populations. The most accurate prediction for young men was with two skinfold, four girth, and two diameter measures (R = 0.88; SE = 0.0069 g/ml); two skinfold and three girth measures accurately predicted body density for middle-aged men (R = 0.84; SE = 0.0074 g/ml).