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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
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Abstract

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.

sample size - medical research - clinical trials - case control study - cohort study - cross-sectional study


Publication History

Article published online:
13 April 2021

© 2021. National Academy of Medical Sciences (India). This is an open access article published by Thieme under the terms of the Creative Commons Attribution-NonDerivative-NonCommercial-License, permitting copying and reproduction so long as the original work is given appropriate credit. Contents may not be used for commercial purposes, or adapted, remixed, transformed or built upon. (https://creativecommons.org/licenses/by-nc-nd/4.0/).

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  • References

  • 1 Johnston KM, Lakzadeh P, Donato BMK, Szabo SM. Methods of sample size calculation in descriptive retrospective burden of illness studies. BMC Med Res Methodol 2019; 19 (01) 9
    CrossrefPubMedGoogle Scholar
  • 2 Uttley J. Power analysis, sample size, and assessment of statistical assumptions—improving the evidential value of lighting research. Leukos 2019; 15: 143-162
    CrossrefGoogle Scholar
  • 3 Crutzen R, Peters GY. Targeting next generations to change the common practice of underpowered research. Front Psychol 2017; 8: 1184
    CrossrefPubMedGoogle Scholar
  • 4 Halpern SD, Karlawish JH, Berlin JA. The continuing unethical conduct of underpowered clinical trials. JAMA 2002; 288 (03) 358-362
    CrossrefPubMedGoogle Scholar
  • 5 Das S, Mitra K, Mandal M. Sample size calculation: Basic principles. Indian J Anaesth 2016; 60 (09) 652-656
    CrossrefPubMedGoogle Scholar
  • 6 Habib A, Johargy A, Mahmood K, Humma H. Design and determination of the sample size in medical research. IOSR J Dent Med 2014; 13: 21-31
    Google Scholar
  • 7 Naing L, Winn T, Rusli BN. Practical issues in calculating the sample size for prevalence studies. medical statistics. Arch Orofac Sci 2006; 1: 19-14
    Google Scholar
  • 8 World Health Organization. Clinical trials. Available at: https://www.who.int/health-topics/clinical-trials/#tab=tab_1. Accessed September 1, 2020
  • 9 Charan J, Biswas T. How to calculate sample size for different study designs in medical research. ? Indian J Psychol Med 2013; 35 (02) 121-126
    CrossrefPubMedGoogle Scholar
  • 10 Süt N. Study designs in medicine. Balkan Med J 2014; 31 (04) 273-277
    CrossrefPubMedGoogle Scholar
  • 11 Sharma SK, Mudgal SK, Thakur K, Gaur R. How to calculate sample size for observational and experimental nursing research studies?. Natl J Physiol Pharm Pharmacol 2020; 10: 1-8
    Google Scholar
  • 12 Baratloo A, Hosseini M, Negida A. El Ashal G. Part 1: simple definition and calculation of accuracy, sensitivity and specificity. Emergency (Tehran) 2015; 3 (02) 48-49
    Google Scholar
  • 13 Negida A, Fahim NK, Negida Y. Sample size calculation guide - part 4: how to calculate the sample size for a diagnostic test accuracy study based on sensitivity, specificity, and the area under the ROC curve. Adv J Emerg Med 2019; 3 (03) e33
    PubMedGoogle Scholar
  • 14 Charan J, Kantharia ND. How to calculate sample size in animal studies?. J Pharmacol Pharmacother 2013; 4 (04) 303-306
    CrossrefPubMedGoogle Scholar
  • 15 Arifin WN, Zahiruddin WM. Sample size calculation in animal studies using resource equation approach. Malays J Med Sci 2017; 24 (05) 101-105
    PubMedGoogle Scholar