A method to construct age references for skewed skinfold data, using Box-Cox transformations to normality.

Document Type

Article

Authors

M A. van 't Hof, University of Nymegen, The Netherlands
J M. Wit, University Children's Hospital, Utracht, The Netherlands
M J. Roede, State University of Limburg, Maastricht, the Netherlands

Abstract

A method is presented to construct age-reference curves for skinfolds and skinfold sums on longitudinal data, using the Box-Cox transformation: (xx - 1 )/X. The method consists of seven steps: 1. Search for X-values producing minimal skewness.2. Calculation of a fitting age curve of X; 3. Transformation of skinfold data at each age with the corresponding X-value and calculation of mean and standard deviation of the transformed data; 4. Drawing eye-fitted smoothed curves through these points; 5. Calculation of percentiles based on the transformed and smoothed means and standard deviations, and plotting these after transformation back to mm. 6. Comparison of percentages of observed measurements in the interpercentile ranges to the target ones; 7. Comparison of the obtained curves with the curves based on the raw data. With this method acceptable Gaussian distribution at each age could be obtained.

Recommended Citation

van 't Hof, M A.; Wit, J M.; and Roede, M J. (1985) "A method to construct age references for skewed skinfold data, using Box-Cox transformations to normality.," Human Biology: Vol. 57: Iss. 1, Article 11.
Available at: https://digitalcommons.wayne.edu/humbiol/vol57/iss1/11