Year : 2020 | Volume : 6 | Issue : 2 | Page : 123--131
Basic principles of sample size calculation
Department of Biostatistics, All India Institute of Medical Sciences, New Delhi, India
The calculation of sample size helps a medical researcher to assess cost, time, and feasibility of his project besides scientific justification and validity. Although frequently reported in journals, the details or the elements of sample size calculation are not consistently provided by the authors. Sample size calculations reported do not match with replication of sample size in many studies. Most trials with negative results do not have a large enough sample size. Hence, reporting of sample size and power needs to be improved. The sample size calculation can be guided by previous literature, pilot studies, and past clinical experiences. The collaborative effort of the researcher and the statistician is required at this stage. Estimated sample size is our best guess. Issues such as anticipated loss to follow-up, large subgroup analysis, and complicated study designs, demand a large sample size to ensure power throughout the trial. The present article will help the reader understand the importance of pilot study in sample size estimation, second understand the relationship between primary objective and sample size of a study, third understand the essential components required in a sample size estimation, and fourth calculate sample sizes using real-life examples using an online software.