# how common are W/H z-scores <-4

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### Anonymous 1501

R.N. Institute of tropical medicine,Charité Berlin

Normal user

8 Oct 2012, 11:49

### Mark Myatt

Frequent user

9 Oct 2012, 13:49

As for mortality, the relationship between WHZ and mortality is complicated by body shape and other factors that vary from place to place. Results from cohort studies will, therefore, be of little use unless your program is in the area where the cohort study was done. The general finding is that is (at these levels of WHZ) mortality risk increases with decreasing WHZ so that a child with a WHZ = -3.9 will likely have a worse prognosis than one with a WHZ = -3.1. So ... it will be quite high.

I hope this helps.

### Mark Myatt

Frequent user

9 Oct 2012, 16:22

I did an analysis of this (for WHO/UNICEF/WFP) some years ago to investigate the implications of raising the MUAC threshold using a databases of 560 nutrition surveys and it the effect was to increase case numbers between 2 - 3 times.

If we assume MUAC is approximately normally distributed then we can do a simple simulation with something like:

=NORMDIST(115,145,15)/NORMDIST(110,145,15)

in a spreadsheet. This gives 2.32 (i.e. the eligible population at MUAC < 115 mm is 2.32 times bigger than the eligible population at MUAC < 110 mm).The new eligible population is the old eligible population (MUAC < 110 mm) with the addition of the children with MUAC = 110 mm, 111 mm, 112 mm, 113 mm, or 114 mm. It is not unreasonable to assume that all of these additional children with have WHZ > -4.

With good coverage we can expect to double our program numbers with about half now above with MUAC > 110 mm and WHZ >= -4. The proportion with WHZ < -4 will, therefore, be about 16.1 / 2.32 = 6.94%.

It is a rough and ready calculation. You should check my logic.

### Mark Myatt

Frequent user

9 Oct 2012, 16:25