Transcription of 19: Sample Size, Precision, and Power
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19: Sample Size, Precision, and Power
Page (C:\DATA\StatPrimer\ B. Gerstman 5/15/03)nsd=422( )nsdd=422( )nsdp=422( )19: Sample Size, Precision, and PowerA study that is insufficiently precise or lacks the Power to reject a false null hypothesis is a waste of time andmoney. A study that collects too much data is also wasteful. Therefore, before collecting data, it is essential todetermine the Sample size requirements of a study. Before calculating the Sample size requirements of a study youmust address some questions. For example: Do you want to learn about a mean? a mean difference? a proportion? a proportion (risk) ratio? an odds ratio?
where ∆ denotes the expected mean difference (or difference worth detecting), n denotes the per group sample size, and σ denotes the standard deviation of the variable (e.g., s, s d, s pooled, s w, etc., depending on your sampling scheme). Example: A study of 30 pairs expects a mean difference of 2. The standard deviation of the paired ...
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