A NARRATIVE REVIEW OF SAMPLE SIZE ESTIMATION FOR QUANTITATIVE EPIDEMIOLOGICAL AND CLINICAL STUDY DESIGNS.

Introduction: Sample size estimation is a crucial step in conducting valid and reliable research. It is the most common question researchers ask biostatisticians, as these investigators often face the problem of estimating the correct sample size for their research. Aim: This article aims to discuss the methods of sample size estimation in quantitative epidemiological and clinical research, presenting key principles and commonly used techniques in a simplified manner. Discussion: Unlike the previously published reviews, this article presents simple, straightforward, and easy-to-understand sample size formulas as well as basic principles on sample size estimation of common study designs in epidemiological and clinical research. In addition, explanations were provided on different statistical theories and concepts, such as outcome variable, confidence level, power, and effect size, which are important considerations in estimating scientifically appropriate sample size. Conclusion: Based on the descriptions and simplified formulas in this article, researchers can easily estimate a sample size that aligns with their study design and outcome measures, enabling more robust and reliable estimates and ensuring that the findings can be generalised to the wider population.