The inheritance of serum cholesterol: adjustment of observed cholesterol levels for age, sex and body weight using inverse-polynomial regression.

Adjustment of observed serum cholesterol levels for biological and environmental variables is an essential step in studying the mode of inheritance of serum cholesterol. Body weight, measured as weight/height2, is found to be an important variable not previously taken into account in regression equations. A method is given for adjusting cholesterol levels for age, sex and body weight, thus obtaining residuals which represent the deviations of cholesterol levels from the mean of the general population for each category of these three factors. The procedure for incorporating into the model other variables, that are found to have a significant effect on cholesterol level, is described. Polynomials and inverse polynomials of degree three fit the data equally well over a restricted range. However, inverse polynomials are chosen as they appear to have a more appropriate shape and are likely to agree better with observed values over a greater age range.