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Calculating a sample size to detect associations between maternal nutrition, HH food security status and dietary diversity.

This question was posted the Assessment and Surveillance forum area and has 4 replies.

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Briony

Nutritionist

Normal user

6 Jul 2015, 07:26

Good morning. Hoping you may be able to help us.... We wish to calculate the association between maternal undernutrition (defined as MUAC <23cm), HH food security status (using HFIAS 4 point scale from food secure to severely insecure) and dietary diversity (using WDDS). We are hoping to explore whether pregnant women from severely food insecure households, or that have low dietary diversity, are more likely to be undernourished. We also wish to explore whether food insecure households are more likely to have low dietary diversity. My statistical skills are not strong, and hoping you may be able to show us how to calculate the required sample size. Information we have includes: 1. Population size: 303,000 total population; 49.4 percent of total are women. We are estimating that around 3 percent of women are pregnant at any one time. 2. We hope to include approx 8-12 villages, which have a population of around 1,100 each. 3. Approx 34 percent of pregnant women are undernourished. 4. HH food insecurity (low, medium and severe) approx 60 percent. And womens dietary diversity scores are approx 5 food groups (range 1-9). Because we know that dietary diversity scores fluctuate with seasonal availability of food, we also hope to collect data over a one year period. Can you clarify the best study design? (its longitudinal, though we have no control group). All thoughts are appreciated! thank you!

Mark Myatt

Frequent user

6 Jul 2015, 14:48

Hello dear all,

We see more and more consumption and sale of plumpy nut by healthy infants. Aware of the consequences that this can have in the long term, I would like to know if there are studies on the short and medium term consequences on healthy children. Or any other information that could serve as a basis for advocacy and awareness.

Thanks

Briony

Nutritionist

Normal user

7 Jul 2015, 11:38

Hi Mark, thank you for your response. Very helpful. However, I am struggling to identify an appropriate study design. A cross sectional would provide us with a snap-shot only (which doesnt factor in the limitations of DDS). Im assuming that the case-control design would be best. However, if we use this design, can we invite women to complete the survey over a one year period? We wish to invite all pregnant women to participate in selected communities over a one year period. Women can form two groups, those undernourished, and those nourished (defined by MUAC) (we were initially considering one group, but this is possible). the purpose of inviting women over a one year period is so we can see how seasonality affects DDS and HFIAS. Each pregnant woman completes one questionnaire only (that said, we could do follow-up questionnaires..). Your thoughts (and others!) are appreciated. thank you!

Anonymous 425

Normal user

7 Jul 2015, 13:20

I think Mark is referring case-control as retrospective. But you are referring cohort study or prospective.

Mark Myatt

Frequent user

8 Jul 2015, 10:50

Sorry, I misunderstood your requirement. A cohort design might work. This can be quite tricky to do as you have to keep track of each member of the cohort and make efforts to follow-up members who have moved away (i.e. because moving might be associated with low DDS or high HFIAS) and to distinguish losses due to deaths (which may also be associated with your risk factors). The cohort design will allow you to look at multiple outcomes (e.g. maternal survival, birth accident. SGS/LBW, &c.). Analysis can be complicated if you want to lag exposures (i.e. see if low DDS twelve, nine, or six months ago affects your outcomes of interest). Another approach which will be simpler and (probably) cheaper would be to do a set of small cross-sectional surveys (e.g. three months apart). This will allow you to track DDS, HFIAS, &c. over time. Analysis could be per survey and (more difficult) over all surveys. What do you think will suit your needs best?

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