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Table 4 Probability of being in each WHO weight band by age

From: Estimating age-based antiretroviral therapy costs for HIV-infected children in resource-limited settings based on World Health Organization weight-based dosing recommendations

  Weight bands
Age (years) 3-5.9 kg 6-9.9 kg 10-13.9 kg 14-19.9 kg 20-24.9 kg 25-34.9 kg 35+ kg
0.5 0.246 0.754 0.000 0.000 0.000 0.000 0.000
1 0.001 0.908 0.091 0.000 0.000 0.000 0.000
2 0.000 0.285 0.706 0.009 0.000 0.000 0.000
3 0.000 0.044 0.842 0.113 0.000 0.000 0.000
4 0.000 0.003 0.593 0.398 0.005 0.000 0.000
5 0.000 0.000 0.262 0.696 0.039 0.003 0.000
6 0.000 0.000 0.070 0.779 0.135 0.016 0.001
7 0.000 0.000 0.011 0.638 0.292 0.057 0.003
8 0.000 0.000 0.001 0.403 0.439 0.147 0.010
9 0.000 0.000 0.000 0.197 0.481 0.293 0.029
10 0.000 0.000 0.000 0.073 0.390 0.464 0.073
11 0.000 0.000 0.000 0.019 0.234 0.586 0.162
12 0.000 0.000 0.000 0.003 0.096 0.591 0.310
13 0.000 0.000 0.000 0.000 0.023 0.465 0.512
  1. Abbreviation: kg kilogram.
  2. Weight-by-age standards were tabulated from the WHO Child Growth Standards for children <5 years and from the CDC Growth Charts for children ages ≥5 years [30, 31]. The equations used to generate these age-specific weight distributions rely on the Lambda-Mu-Sigma parameters: the median (M) weight, the generalized coefficient of variation (S), and the power in the Box-Cox transformation (L) [32, 34]. To account for lower weights among HIV-infected children relative to the general population of same age, the age-specific weight distributions for HIV-infected children were shifted to the -1.5 z-score of the general population distributions [33]. The HIV-infected median weight-for-age values (MHIV) were calculated at half-year intervals, where MHIV was equal to the value M*(1 + LSZ)(1/L). The coefficient of variation (SHIV) was assumed to be equal to that of children of the same age in the general population. Z-scores for the upper and lower bounds of the WHO-specified weight intervals for ARV dosing (3 kg, 5.9 kg, 6 kg, 9.9 kg, 10 kg, 13.9 kg, 14 kg, 19.9 kg, 20 kg, 24.9 kg, 25 kg, and 34.9 kg) were calculated by gender for children ages 0–13 years old, as follows: the z-score of the bound of interest, X, equals ((X/MHIV)L -1)/L*SHIV. The Norm.S.Dist(z,1) Excel function was used to convert z-scores into cumulative probability estimates. The probability of being in each weight band (by age and gender) was calculated as the cumulative probability of being below the upper bound of the weight band subtracted by the cumulative probability of being below the lower bound of the weight band (or the area under the curve within the upper and lower bounds). Results shown above assume an equal proportion of males and females.