Principles of Statistics for Surgeons III: Factors Influencing Sample Size Estimation


  • Panuwat Lertsithichai Department of Surgery, Ramathibodi Hospital, Mahidol University, Bangkok, Thailand


sample size, estimation, factors


The present article, the third in a series, describes some important ideas underlying the practice of sample size estimation. These include types I and II errors, the effect size, and data variability. Each of these ideas is described and illustrated in some detail without too much technical development, and should be relatively easy to understand for most surgeons. In particular, important concepts in elementary statistics are highlighted and should be useful for self-study. The necessity of some prior context-specific knowledge, when estimating the sample size, is emphasized. Simple numerical examples are presented at the end of the article to strengthen the emphasis. We hope the reader will be sufficiently informed in preparation for consultations with statisticians when such needs arise.


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1. Charles P, Giraudeau B, Dechartres A, Baron G, Ravaud P.
Reporting sample size calculation in randomised controlled
trials: review. Br Med J 2009;338;b1732;doi:10.1136/

2. Spiegelhalter DJ, Abrams KR, Myles LP. Bayesian approaches
to clinical trials and health-care evaluation. Chichester:
John Wiley & Sons, Ltd; 2004. p. 181-249.

3. Lertsithichai P. Variability and randomness in medical
research. Thai J Surg 2010;31:1-6.

4. Casella G, Berger RL. Statistical inference. 2nd ed. California:
Duxbury Press; 2002. p. 236-9.

5. Machin D, Campbell MJ. Design of studies for medical
research. Chichester: John Wiley & Sons, Ltd; 2005.




How to Cite

Lertsithichai P. Principles of Statistics for Surgeons III: Factors Influencing Sample Size Estimation. Thai J Surg [Internet]. 2012 Jun. 29 [cited 2022 Dec. 10];33(2). Available from:



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