# Using length/height to estimate Age of 6-59 month old children in high Stunting level countries

This question was posted the Assessment and Surveillance forum area and has 7 replies.

### Anonymous 411

Nutritionist

Normal user

5 May 2011, 19:49

### Anonymous 118

Nutrition Advisor

Normal user

5 May 2011, 20:19

### Mark Myatt

Frequent user

6 May 2011, 10:23

### Anonymous 402

Normal user

15 Dec 2011, 22:40

### Mark Myatt

Frequent user

16 Dec 2011, 09:21

```
For boys :
Median L/A at 6 months = 67.6
Median H/A at 59 months = 109.4
For girls :
Median L/A at 6 months = 65.7
Median H/A at 59 months = 108.9
Average ("sex-combined"):
Median L/A at 6 months = (67.6 + 65.7) / 2 = 66.7
Median H/A at 59 months = (109.4 + 108.9) / 2 = 109.2
```

That looks like 67 to 109 cm to me.
Remember that the WGS is about ideal conditions. On EN-NET we don't often find ourselves dealing with populations that have or are experiencing conditions ideal for growth. That means that using a threshold of 67 cm will exclude a lot of 6 month old children. Far more that 50% because 67 cm will (by definition) exclude half of six months olds. We can expect "our" children to be a bit below the WGS. Let us say 1 SD below. What happens then?
```
For boys :
Median L/A - 1 SD at 6 months = 65.5
Median H/A - 1 SD at 59 months = 105.3
For girls :
Median L/A - 1 SD at 6 months = 63.5
Median H/A - 1 SD at 59 months = 104.7
Average ("sex-combined"):
Median - 1 SD L/A at 6 months = (65.5 + 63.5) / 2 = 64.5
Median - 1 SD H/A at 59 months = (105.3 + 104.7) / 2 = 105.0
```

That's where the 65 cm comes from.
The 110 cm is a hang-over from the NCHS reference. I'm not to worried about that being quite a way above 105 cm because SAM is mostly a disease of far smaller and younger kids (unless you are using something weird like W/H in your SAM case-definition and fill you program up with healthy long-legged children).
The initial question mentions 60 cm and 100 cm. These are, IMO, better than 65-110 cm and 67-110 cm for the contexts that we work in.
### Bradley A. Woodruff

Self-employed

Technical expert

16 Dec 2011, 13:58

### André Briend

Frequent user

16 Dec 2011, 16:16

### Mark Myatt

Frequent user

16 Dec 2011, 16:54

```
Bairagi R, Effects of bias and random error in anthropometry
and in age on estimation of malnutrition, Am J Epidemiol,
1986;123(1):185-91
```

This shows that W/A and H/A are very susceptible to errors in age. Children grow fast and this means that small errors in estimating age may lead to large errors in indicator values. In famine, and situations where displacement and familial separation are common, field workers are often required to estimate the age of children based on little or no information. Estimates “by eye” are biased by assumptions about the relationship between height and age which are likely to be invalid in situations of nutritional stress. In these cases, indicator values will be subject to errors, probably systematic and upwards, that are products of random errors in estimating age and systematic errors in estimating age that may be influenced by growth failure.
This is a rather long winded way of saying that I agree completely with Brad that if you are looking at stunting (or underweight) then you should take the time to make and test local calendars ... not just for eligibility but also for ascertaining age with some accuracy, Don't rely on maternal report as these are usually biased towards whole years. When I was a child I remember saying things like "I am six years, eight months, and elven days old" when asked my age (I'm sure we all did this). My mum would say "six" or "six and a half". That sort of rounding will (if widespread and typical) increase the estimate of the prevalence of stunting just by rounding error.
I think that André has it right too (including regarding maternal report with the youngest children).If you have any problem posting a response, please contact the moderator at post@en-net.org.