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posted on 08.12.2016, 11:58 authored by Emmanuel GrelletyEmmanuel Grellety

The WHO standards are available on the website of WHO (http://www.who.int/childgrowth/en/). You find there the software Anthro2005 for calculation of individual data (Anthro2005).

 

For calculating the z-scores of the new standards the LMS procedure is used. The principle is to get from a table for a certain age and sex 3 values (LMS) which are put into a formula For example WAZ = ((weight/M)^L-1)/(L*S)) e.g.:

 

Female, 9kg, 365 days => L = -0.2022, M = 8.9462, S = 0.12267

 

WAZ = ((9/M)^L-1)/(L*S) = ((9/8.9462)^-0.2022-1)/(-0.2022*0.12267) = 0.04885 Z-scores

 

On the WHO website you find only the LMS values for each month.

Wt                L                   M                  S

 9            -0.2022          8.9462        0.12267        0.048847178

 

To calculate the actual weight from the LSM statistics at any cut off point use the following formula:

wt = M * ((Z * S * L) +1)^(1/L)

Where Z = Zscore you are trying to obtain

This is the reverse of the formula to calculate WAZ etc.

And will give the standard to more decimal places for interpolation [purposes

I have taken 10 boys and 10 girls at 0.5 cm intervals from 60 to 110cm in height with weight for height mean at -1Z with SD or 1.0.

These are in the sheet WFH_Population.

For the simulation I have now added a random variable to the weight or the height in the POP_weight and the POP_height sheets.

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