Sample size refers to the total number of participants whose responses are collected and analyzed in a given study. In quantitative research, sample size is a critical design decision: too small a sample produces unreliable estimates with wide margins of error, while an appropriately sized sample supports statistically significant conclusions that can be generalized to a target population. Researchers calculate required sample sizes using factors such as confidence level, margin of error, expected variance, and population size. In mixed-method research, sample size considerations differ by method, with qualitative components typically requiring far fewer participants to reach thematic saturation than quantitative components require for statistical power.