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Before and an after holiday effect-on nutritional indices

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Asmelash

Nutritionist /NRC

Normal user

7 Oct 2015, 14:37

Dear En-net members,

We have currently conducted a nation wide SMART survey with 5-7 days Muslim Eid holiday in break where we got more than 80% of the data set just before and the remaining 20%afterwards. As the holiday might have contributed for any weight gain in the targeted study group(U5 and WRA), we were contemplating to understand if there will be any meaningful statistical difference between the two and how best to measure the effect that i.e prospective or retrospective or suitable statistical parameters for before and after 'event'/exposure ?

Any advice and guidance in this regard is highly appreciated.

My best regards.

Mark Myatt

Consultant Epideomiologist

Frequent user

8 Oct 2015, 08:44

It is possible to assess the difference between prevalence estimates returned by two surveys. A simple approach is to estimate the standard error in each survey:

    SE = (UCL - LCL) / (2 * 1.96)

then poole the two SEs:

    PooledSE = sqrt(SE1^2 + SE2^2)

and calculate a z-test:

    z = abs(prevalence1 - prevalence2) / PooledSE

The p-value is taken from the normal distribution (if abs(z) > 1.96 the p < 0.05).

You use an estimation approach:

    difference = abs(prevalence1 - prevalence2)
    95% CI = difference +/- 1.96 * PooledSE


I think you may have an issue with the sample size in the second "survey". The SE for the second "survey" will be wide. This means that you will not see a significant difference unless the difference is very large.

I hope this is of some use.

Mark Myatt

Consultant Epideomiologist

Frequent user

8 Oct 2015, 09:13

Just remembered ...

You will be able to get a bit more power if you use the mean MUAC (or mean WHZ, WAZ, HAZ) and test for differences between means rather than prevalences.

I still think you will have sample size issues.

Asmelash

Nutritionist /NRC

Normal user

8 Oct 2015, 12:06

Dear Mark,

Thank you so much for the guidance. I will use both methods see which one yield for any statistical difference, of course the last round sample is too small if any.

On another note, I saw in one of your conversation the value of and how to form a combined nutritional index for further analysis(WFH, WFA and HFA) but I seem to be at loss trying to locate it and get the information.

I will appreciate it if you can direct me to the link in your best convenient time.

Warmest regards.

Mark Myatt

Consultant Epideomiologist

Frequent user

8 Oct 2015, 15:20

Happy to help.

I think you mean the Composite Index of Anthropometric Failure (CIAF).

You can find the original article here.

Mark Myatt

Consultant Epideomiologist

Frequent user

8 Oct 2015, 15:22

Also, see here.

Mark Myatt

Consultant Epideomiologist

Frequent user

13 Oct 2015, 13:27

Thanks to Chris Hillbruner (Decision Support Advisor - FEWS NET) who writes ...

This is another interesting example of using CIAF, in this case to explore the relationship between mortality risk and the presence of multiple anthropometric deficits.

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