This document discusses sample size determination and calculation. It defines sample size as the subset of a population chosen for a study to make inferences about the total population. The key factors in determining sample size are the desired level of accuracy, allowing for appropriate analysis, and validity of significance tests. The document provides formulas and methods for calculating sample size for different study designs and populations, including using formulas, readymade tables, nomograms, and computer software. Accurately determining sample size is essential for research.