CC BY-NC-ND 4.0 · Ann Natl Acad Med Sci 2021; 57(02): 074-080
DOI: 10.1055/s-0040-1722104
Review Article

Sample Size Calculation in Medical Research: A Primer

Jaykaran Charan
1   Department of Pharmacology, All India Institute of Medical Sciences, Jodhpur, Rajasthan, India
Rimplejeet Kaur
1   Department of Pharmacology, All India Institute of Medical Sciences, Jodhpur, Rajasthan, India
Pankaj Bhardwaj
2   Department of Community and Family Medicine, All India Institute of Medical Sciences, Jodhpur, Rajasthan, India
Kuldeep Singh
3   Department of Paediatrics, All India Institute of Medical Sciences, Jodhpur, Rajasthan, India
Sneha R. Ambwani
4   Department of Pharmacology, All India Institute of Medical Sciences, Jodhpur, Rajasthan, India
Sanjeev Misra
5   All India Institute of Medical Sciences, Jodhpur, Rajasthan, India
› Author Affiliations
Funding None.


Quality of research is determined by many factors and one such climacteric factor is sample size. Inability to use correct sample size in study might lead to fallacious results in the form of rejection of true findings or approval of false results. Too large sample size is wastage of resources and use of too small sample size might fail to answer the research question or provide imprecise results and may question the validity of study. Despite being such a paramount aspect of research, the knowledge about sample size calculation is sparse among researchers. Why is it important to calculate sample size; when to calculate it; how to calculate it and what details about sample size calculation should be reported in research protocols or articles; are the lesser known basics to majority of researchers. The present review is directed to address these aforementioned fundamentals about sample size. Sample size should be calculated during the initial phase of planning of study. Several components are required for sample size calculation such as effect size, type-1 error, type-2 error, and variance. Researchers must be aware that there are different formulas for calculating sample size for different types of study designs. The researcher must include details about sample size calculation in the methodology section, so that it can be justified and it also adds to the transparency of the study. The literature about calculation of sample size for different study designs is scattered over many textbooks and journals. Scrupulous literature search was conducted to find the passable information for this review. This paper presents the sample size calculation formulas in a single review in a simplified manner with relevant examples, so that researchers may adequately use them in their research.

Publication History

Article published online:
13 April 2021

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