Sample size refers to the number of individuals or observations included in a research study. It is a crucial consideration in research design because it directly impacts the reliability and validity of study findings. A larger sample size generally provides more reliable results and allows for more generalizable conclusions to be drawn. Researchers must carefully determine an appropriate sample size based on factors such as the research question, study design, statistical power, and budget constraints. A sample size that is too small may lead to biased or inconclusive results, while a sample size that is too large may waste resources and time. Overall, selecting an appropriate sample size is essential for the successful execution and interpretation of research studies.