When we are using already available records, in a retrospective cohort study the sample size calculation to be done in which formula?

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David Eugene Booth

Under your conditions I would use all the records I had. This is not a sampling situation. D. Booth

Sameera Ranasinghe

Thanks a lot.But won't it affect the power of the study.Of course power would be higher.@David Eugene Booth

No you are dealing with a population NOT a sample if you use all the records as I would advise.