Required sample size for comparing two independent means

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Abstract

Sample size calculation in a planning phase is still uncommon in Russian research practice. This situation threatens validity of the conclusions and may introduce Type I error when the false null hypothesis is accepted due to lack of statistical power to detect the existing difference between the means. Comparing two means using unpaired Students’ ttests is the most common statistical procedure in the Russian biomedical literature. However, calculations of the minimal required sample size or retrospective calculation of the statistical power were observed only in very few publications. In this paper we demonstrate how to calculate required sample size for comparing means in unpaired samples using WinPepi and Stata software. In addition, we produced tables for minimal required sample size for studies when two means have to be compared and body mass index and blood pressure are the variables of interest. The tables were constructed for unpaired samples for different levels of statistical power and standard deviations obtained from the literature.

About the authors

A. M. Grjibovski

Northern State Medical University;
North-Eastern Federal University

Author for correspondence.
Email: Andrej.Grjibovski@gmail.com
ORCID iD: 0000-0002-5464-0498

Andrej M. Grjibovski

Arkhangelsk

Russian Federation

M. A. Gorbatova

Northern State Medical University

Email: marigora@mail.ru
ORCID iD: 0000-0002-6363-9595

Maria A. Gorbatova

Arkhangelsk

Russian Federation

A. N. Narkevich

Рrofessor V. F. Voyno-Yasenetsky Krasnoyarsk State Medical University

Email: narkevichart@gmail.com
ORCID iD: 0000-0002-1489-5058

Artem N. Narkevich

Krasnoyarsk

Russian Federation

K. A. Vinogradov

Рrofessor V. F. Voyno-Yasenetsky Krasnoyarsk State Medical University

Email: vinogradov16@yandex.ru
ORCID iD: 0000-0001-6224-5618

Konstantin A. Vinogradov

Krasnoyarsk

Russian Federation

References

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