The Confusing Terminology "Sample Size"​ in Evidence Based Medicine and How it Affects Your Research
13th September 2022 By MARS Research Hub

What is Evidence-Based Medicine?

Evidence-based medicine is a systematic approach to clinical decision-making that uses the best available evidence from research and patient values. This approach is used by physicians, nurses, pharmacists, and other healthcare professionals in their everyday practice. Evidence-based medicine relies on high-quality scientific data from medical research studies as well as individual patient preferences.

The goal of evidence-based medicine is to achieve the best possible health outcomes for patients by integrating the best research evidence with clinical expertise and patient values.

Evidence-Based Research and the Importance of Sample Size Calculation

The sample size calculation is an important step in any research methodology. The calculation is needed to determine the accuracy of the research and how many participants are needed for the study. The sample size calculation is a way to make sure that the study is reliable and includes enough data to provide an accurate result. A sample size estimate yields a range of information, traditionally expressed as a minimum number of cases (i.e., participants).

Sample size estimates are necessary for decision-making and to determine the size of subjects in a clinical trial. For instance, in a clinical trial, the sample size estimate is needed to determine how many participants are needed for the study to ensure that the findings are applicable to the population of interest, rather than to just a non-representable sample of that population.

Estimating Sample Size by Power Analysis

Power analysis is a statistical technique used to determine the sample size required for a statistical study. The power of a study refers to the probability that the study will find an effect that is actually present in the population being studied.

Various resources reported that a minimum of 80% is essential given the available resources and ethical considerations. Power is typically considered when determining what sample size to use for a study.

How to Calculate Sample Size for a Randomized Control Trial Design?

A randomized control trial is used to test the efficacy and/or safety of a new drug or a treatment.

In its simplest scenario, to calculate the sample size, we need to know the following:

-The proportion of subjects who will be assigned to each treatment group.

- The probability that each subject will respond (or not) to the treatments.

- The degree of precision desired in estimating the difference between treatments.

The precision can be expressed as a standard error or confidence interval.

Recommended resources for sample size calculation.

There are tons of sample size calculation books and resources, at MARS, the top 3 books we rely on for sample size calculations are:


  • Sample Size Calculations for Clustered and Longitudinal Outcomes in Clinical Research by Chul Ahn · Moonseoung Heo · Song Zhang
  • Sample Size Calculations in Clinical Research: Edition 3 by Shein-Chung Chow · Jun Shao · Hansheng Wang · Yuliya Lokhnygina
  • Clinical Trial Data Analysis Using R By Ding-Geng (Din) Chen, Karl E. Peace



Conclusion: Confused with all the terminology in evidence-based medicine and related sample size essentials for the generalizability of your research results? This article is for you!