The LMS method for constructing normalized growth standards.

It is now common practice to express child growth status in the form of SD scores. The LMS method provides a way of obtaining normalized growth centile standards which simplifies this assessment, and which deals quite generally with skewness which may be present in the distribution of the measurement (eg height, weight, circumferences or skinfolds). It assumes that the data can be normalized by using a power transformation, which stretches one tail of the distribution and shrinks the other, removing the skewness. The optimal power to obtain normality is calculated for each of a series of age groups and the trend summarized by a smooth (L) curve. Trends in the mean (M) and coefficient of variation (S) are similarly smoothed. The resulting L, M and S curves contain the information to draw any centile curve, and to convert measurements (even extreme values) into exact SD scores. A table giving approximate standard errors for the smoothed centiles is provided. The method, which is illustrated with US girls' weight data, should prove useful both for the construction and application of growth standards.