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Using Road to Health Charts, is a percentile cut-off commonly used to indicate growth problems

This question was posted the Prevention and treatment of moderate acute malnutrition forum area and has 5 replies. You can also reply via email – be sure to leave the subject unchanged.

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Hatty Barthorp

Global Nut Advisor / GOAL

Normal user

31 Jan 2014, 11:02

Just wondering, when using RtH charts, is there a commonly used percentile cut-off or benchmark used, below which would indicate growth problems, or should they be used merely to track growth trajectory and if growth faltering is observed, this should be the only measure used to indicate a problem?

Mark Myatt

Consultant Epideomiologist

Frequent user

31 Jan 2014, 11:29

You would not really want W/A to drop much below -2 z (roughly P3). The usual approach with GMP data is to look for deviations from the expected growth curve. A child may track the growth curve even when they have a low W/A. This is usually OK. Dropping away from the growth curve is "growth faltering". When you see this then take MUAC. If MUAC is < 115 mm then refer to CMAM. If MUAC >= 155 mm then counsel and refer to appropriate support services.

Mark Myatt

Consultant Epideomiologist

Frequent user

31 Jan 2014, 11:31

Oops ... meant 115 mm.

Not sure why the posts appears twice.

Hatty Barthorp

Global Nut Advisor / GOAL

Normal user

31 Jan 2014, 12:11

Hi Mark - Thanks for the speedy response. Do you per chance have a ref' I could look at illustrating the corresponding values of percentiles to z-scores?

Mark Myatt

Consultant Epideomiologist

Frequent user

31 Jan 2014, 12:58

The reference distributions are very nearly normally distributed so you can expect (e.g.) P16 to be at -1 z-score (we often use P15) and P2.5 to be at -1.96 z-scores. Here is a short table showing how z and p are related:

      z    p
   ---- ----
    0.0  0.50 <- P50
   -0.1  0.46
   -0.2  0.42
   -0.3  0.38
   -0.4  0.34
   -0.5  0.31
   -0.6  0.27
   -0.7  0.24
   -0.8  0.21
   -0.9  0.18
   -1.0  0.16 <- P15 (or thereabouts)
   -1.1  0.14
   -1.2  0.12
   -1.3  0.10
   -1.4  0.08
   -1.5  0.07
   -1.6  0.05
   -1.7  0.04
   -1.8  0.04
   -1.9  0.03 <- P3 (or thereabouts)
   -2.0  0.02
   -2.1  0.02
   -2.2  0.01 <- P1 (or thereabouts)
   -2.3  0.01
   -2.4  0.01
   -2.5  0.01
   -2.6  0.00
   ----  ----

Software like EpiInfo, ANTHRO, ENA, &c. will calculate z-scores and percentiles for you.

Tables are available ... for example that give percentiles:

http://www.who.int/childgrowth/standards/en/

Any help?

Hatty Barthorp

Global Nut Advisor / GOAL

Normal user

31 Jan 2014, 14:40

Perfect - just was I was looking for! Thanks Mark

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