Approach to sample size calculation in medical research

Adequate sample size is of paramount importance in medical research. Inadequate number of subjects in a study may lead to inconclusive results and erroneous interpretation. This necessitates estimation of sample size for a research project. There are formulae for calculation of sample size for different study designs. A researcher can manually compute sample size using these formulae. Alternatively, there are several statistical softwares and online calculators, which can compute sample size for various research designs. Common types of study designs in medical research are estimation of a proportion or a mean in a defined population; and hypothesis testing for a difference in two qualitative (proportions) or two quantitative outcomes (means). For each type of study design, investigator needs to have some a priori information like precision, acceptable limits of α & β error, confidence level and effect size.