Say I'm designing a retrospective study (where I'd collect data from various schools for the last 5 years) to see if consuming milk can contribute to childhood obesity. How do I decide on how many schools to visit? If I remember my stats correctly, in general, the goal is to achieve 95% confidence in our results, right? So how many schools would I have to collect data from so that I will have 95% confidence in the outcome of the study?

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    $\begingroup$ Related Question $\endgroup$
    – Rory M
    Feb 15, 2013 at 23:41
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    $\begingroup$ You might consider posting this on Cross Validated, but as shigeta mentioned, you'd need to provide more details. $\endgroup$
    – blep
    Feb 16, 2013 at 9:15
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    $\begingroup$ Maybe this isn't the answer you're looking for... nobody who has ever done a study like this has wanted to have fewer subjects than they could get. I'd say the answer to your question could just be 'funding' $\endgroup$
    – shigeta
    Feb 18, 2013 at 2:21
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    $\begingroup$ About experimental design and is a purely statistical question. $\endgroup$ Oct 22, 2013 at 11:54
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    $\begingroup$ I'm voting to close this question as off-topic because this question is about statistics, not biology. $\endgroup$
    – Remi.b
    Jun 29, 2017 at 15:37

1 Answer 1


Could be as much as possible – using multistage sampling. But it all depends on how much you are willing to spend, and your time constraint.

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    $\begingroup$ Welcome to Biology.SE! This does not seem to answer the question. Please add some more details and references to your answer. $\endgroup$ Jun 29, 2017 at 15:05

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