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Sample size can be calculated in different ways, for instance, using a margin of error and confidence level or doing power analysis etc.

What would be some matters to take into consideration when choosing a method of sample calculation?

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up vote 3 down vote accepted

The first and most important thing to consider is what question you are trying to answer. If you are estimating something using a confidence interval then margin of error is important. If you are doing a test of significance then power is important. If your main goal is something else, then consider what goes into that question.

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I think you are confusing two things here. Power analysis, at least a priori power analysis, requires that you assume things prior to having data. This is, at least in part, to find out how much data you will need to get, and whether it is practical to do so. Post-hoc power analysis is frowned on, and there have been posts here about that. In a power analysis, you can assume a CI or a MOE or other things, and that really shouldn't matter, as far as I can see.

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