Prediction of body density from skinfold thickness in elderly subjects: are the existing equations valid?

In 33 healthy elderly subjects, body density was measured using hydrodensitometry and predicted from the sum of four skinfold thicknesses. In the men, mean measured density was 1.045 kg/l and mean predicted density 1.041 kg/l, with bias and limits of agreement 0.004 (+/- 0.016) kg/l and 95% confidence interval (CI) for the difference 0.001-0.008 kg/l. In the women, mean measured density was 1.012 kg/l and mean predicted density 1.020 kg/l, and 95% CI for the difference was -0.016-0.000 kg/l. The bias was therefore in the opposite direction in women than men, and limits of agreement were wider (-0.008 +/- 0.030 kg/l) in the women. Biases in prediction of density lead to systematic error in estimation of body fatness in elderly subjects, and this systematic error is more likely to be of practical significance in women than men.