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I am doing an assignment for 3rd year med. The methods in the paper claims 93% power but sample size is only 20 people. If a study is sufficiently powered, is there anything i should be concerned about when interpreting the results of the study?

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With that few observations every single observation that is a bit "weird" will quickly become very influential, that is, that person will have a very large influence on the size and direction of the effect. That may be fine, and that may not be fine, depending on the circumstances.

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  • $\begingroup$ In addition another question to consider is whether the assumptions are realistic. By claiming that one assumes a sufficiently large effect size (no matter how unrealistic), a researcher can pretend to have a well-powered study. There may be an incentive to be overoptimistic, because funding and ethics committee approval usually depends on the trial having a realistic chance of achieving its goal and some researchers may be tempted to do this (and would hope that even if there is realistically no power, they will "know it when they see it"). $\endgroup$
    – Björn
    Jan 8, 2018 at 11:57
  • $\begingroup$ I will add to @Björn's comment that even if the sample size was calculated to provide 80% power, there is NOT an 80% chance that the trial will be successful. The effect size can be different than planned. The variability can be different than planned. Etc. Note: when performing a sample size calculation, uncertainty in the parameters is usually/unfortunately not accounted for. $\endgroup$
    – ocram
    Jan 8, 2018 at 12:38

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