How to assess power and sample size

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Cadeddu M, Farrokhyar F, Thoma A, Haines T, Garnett A, Goldsmith CH, Evidence-Based Surgery Working Group. Users' guide to the surgical literature: how to assess power and sample size. Laparoscopic vs open appendectomy. Can J Surg 2008;51(6):476-82.


A common difficulty encountered by surgeons is the broad range of treatment choices available for a surgical condition. Observational studies and small randomized trials account for a large proportion of the surgical literature. There are many reasons for this, but the clinician is left with evidence from small studies on which to base his or her practice. How can a surgeon know from a study that reports no difference between treatments whether the study group was too small to detect any difference?

This question refers to whether a study is adequately powered to answer the research question. We provide a succinct overview of power issues in surgical studies to better equip clinicians to assess the adequacy of a study’s sample size and to determine whether its conclusions are valid and can be used to guide surgical practice.

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