Tuxford's index of nutrition; a convenient nomogram.

Tuxford's index, first described in 1917, was based on measurements, made in 1909 and 1910, of half a million elementary-school children in various parts of England (Tuxford, 1917). It is the ratio of weight to height graduated by age to allow for the changes which o a u r in the ratio with age. The index was again described in 1939, and formulae for use with British units were added to the original metric formulae (Tuxford, 1939). In 1942 Tuxford devised a new index to fit the proportions of London school-children as shown by the 1938 measurements (Tuxford, 194.2). The new formula for boys is and for girls W 336-m W 308-m-x-, H * Y H 235 where W is weight in lb., H height in in. and m age in months. There are similar formulae in metric units. The index was devised and the numerical constants in the age factor chosen so that the value of the index for average heights and weights is 1-0 at all ages considered. Children heavier than average for their height and age have an index greater than 1-0, those lighter than average for their height and age an index less than 1.0. Although simplicity of calculation was one of the objects of the author, the formula is still somewhat tedious to use with a large number of children. We therefore thought that a nomogram, or line chart, from which the values of the index could be read directly, might be welcomed by nutrition workers. METHOD The nomogram The nomogram is shown in Fig. I. A straight line through the observed height and weight meets the pivot line at the ratio of weight to height. The line is then swung round this point until it passes through the appropriate age, and the point where the line crosses the index line gives the result. Example. A boy aged 8 years has a height of 40 in. and a weight of 48 lb. A straight line from 40 in. through 48 lb. meets the pivot line at 1.2. A second straight line from 1-2 on the pivot line through 8 years on the boys' scale meets the index line at 1.067. It is not necessary to read the value on the pivot line.