European height and weight growth charts commonly extend from the 3rd to the 97th centile, whereas in North America the extremes are usually the 5th and 95th centiles. There is no good reason for the difference, and neither chart is particularly useful for screening owing to the high false positive rate associated with a cut off based on the lowest centile. The World Health Organisation's international growth reference uses cut offs based on standard deviation scores rather than centiles, which are more suitable for the extremes of growth status seen in the developing world. This chart, however, is incompatible with charts based on centiles. sere a unified growth chart is proposed: it has nine rather than seven centiles, and they are spaced two thirds of a standard deviation score apart rather than the more usual unit spacing. This gives a set of curves very like the conventional 3rd to 97th centiles, but with additional curves at 2.67 standard deviation below and above the mean (roughly the 0.4th and 99.6th centiles). The 0.4th centile is a more practical cut off for screening purposes than the 3rd or 5th centile.
