A comparison of different approaches for fitting centile curves to birthweight data

Centile charts, plotted by week of gestational age, are widely used clinically to decide whether a child is 'small-for-dates', indicating that there may have been some cause of intra-uterine growth retardation. A variety of different statistical techniques have been proposed for constructing centile charts. Some methods are distribution free and work on the basis of obtaining and then smoothing the empirical centiles. In others the centiles are calculated assuming a Normal distribution either of the raw data or of transformed data. In Scotland the details of each maternity admission are entered onto an SMR2 form and these records are stored centrally by the Scottish Health Service. A data set consisting of all live births occurring in Scottish hospitals between 1980 and 1992 is used to compare different approaches to constructing centile charts.