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The use of the NCHS standard to assess weight-for-height in children is equivalent to expressing the child’s weight and height, in the ratio W/Hp, as a fraction of the NCHS median W/Hp for age, where the power p of height changes with age. It falls from a value of 3 at birth to 1.5 at 18 months, and then rises to 3 again by 11 years. Its discontinuous pattern of change in the second six months of life leads to poten­tially misleading assessments of weight-for-height in very tall or very short children. Weight for height standards in general, and the NCHS standard in particular, should not be used to assess weight-for-height in young children. The index W/H2, expressed as a fraction of the NCHS median W/H2 for age, should be used instead.