Determining sample size involves several key factors:
Study Design: The type of study (e.g., randomized controlled trial, cohort study, case-control study) influences the sample size calculation. Effect Size: This is a measure of the strength of the relationship between variables. A larger effect size generally requires a smaller sample size, while a smaller effect size requires a larger sample size. Power: The probability that the study will detect an effect if there is one to be detected. Commonly, a power of 0.8 (80%) is used. Significance Level: The probability of rejecting the null hypothesis when it is true, commonly set at 0.05 (5%). Variability: The degree of variation in the population being studied. Higher variability typically requires a larger sample size to detect a true effect.
