Clin Orthop Surg.  2013 Sep;5(3):235-242. 10.4055/cios.2013.5.3.235.

How to Calculate Sample Size and Why

• Kim J
• Seo BS

• KMID: 1705551
• DOI: http://doi.org/10.4055/cios.2013.5.3.235

Abstract

WHY: Calculating the sample size is essential to reduce the cost of a study and to prove the hypothesis effectively. HOW: Referring to pilot studies and previous research studies, we can choose a proper hypothesis and simplify the studies by using a website or Microsoft Excel sheet that contains formulas for calculating sample size in the beginning stage of the study. MORE: There are numerous formulas for calculating the sample size for complicated statistics and studies, but most studies can use basic calculating methods for sample size calculation.

Keyword

Sample size

MeSH Terms

Chi-Square Distribution
*Research Design
*Sample Size
Statistics as Topic/*methods

Figure

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  Fig. 1 An example of sample size calculation for a binary outcome superiority trial. Adaped from http://www.sealedenvelope.com/power/binary-superiority/ with permission from Sealed Envelope.

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  Fig. 2 The formula for a binary outcome superiority trial. Adaped from http://www.sealedenvelope.com/power/binary-superiority/ with permission from Sealed Envelope.

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  Fig. 3 Another example of sample size calculation for a binary outcome superiority trial. Adapted from http://department.obg.cuhk.edu.hk/.

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  Fig. 4 The results of Fig. 3. Adapted from http://department.obg.cuhk.edu.hk/.

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  Fig. 5 An example of sample size calculation for a continuous outcome superiority trial. Adaped from http://www.sealedenvelope.com/power/binary-superiority/ with permission from Sealed Envelope.

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  Fig. 6 Another example of sample size calculation for a continuous outcome superiority trial.

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  Fig. 7 Author's Excel file for sample size calculation for various tests.

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  Fig. 8 Author's Excel file for sample size calculation; chi-squared test.

Reference

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2. Petrie A. Statistics in orthopaedic papers. J Bone Joint Surg Br. 2006; 88(9):1121–1136.

3. Sexton SA, Ferguson N, Pearce C, Ricketts DM. The misuse of 'no significant difference' in British orthopaedic literature. Ann R Coll Surg Engl. 2008; 90(1):58–61.

4. Wikipedia. Effect size [Internet]. Wikipedia;2013. cited 2013 May 22. Available from: http://en.wikipedia.org/w/index.php?title=Effect_size&oldid=554920483.