5. CONSTRUCTION OF THE WEIGHT-FOR-LENGTH AND WEIGHT-FOR- HEIGHT STANDARDS

The construction of the weight-for-length (45 to 110 cm) and weight-for-height (65 to 120 cm) standards followed a procedure similar to that applied to constructing the length/height-for-age standards (see section 3.1). To fit a single model, 0.7 cm was added to the cross-sectional height values. This was the average difference found between length and height in 1625 children aged 18 to 30 months measured for both length and height. After the model was fitted, the weight-for-length centile curves in the length interval 65.7 to 120.7 cm were shifted back by 0.7 cm to derive the weight-for-height standards corresponding to the height range 65 cm to 120 cm. There was an important distinction between age versus length/height as the x-axis variable. Although the study was designed to give a relatively constant number of observations per age group, this was not the case for length/height. Therefore, in contrast to the square tail of the uniform age distribution there was a light upper tail for the height distribution. The age-based indicator curves were constructed using all available data (0 to 71 months) but the resulting standards were truncated at 60 completed months to avoid the right-edge effect (Borghi et al., 2006). The construction of the weight-for-height standards followed this precedent by using the full range of available heights independently of age. The decision about where to set the upper limit for the weight-for-height standards was influenced b