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Sample size in clinical research: why it matters and how it is determined

Sample size is a critical component of clinical research that directly influences the validity, reliability, and interpretability of study findings. Determining an appropriate sample size is not merely a statistical exercise but a multidisciplinary decision involving clinical relevance, study design, variability, and ethical considerations. An inadequately powered study may fail to detect meaningful treatment effects, whereas an excessively large study may expose unnecessary numbers of participants to interventions and increase study costs. This article provides a practical overview of why sample size matters in clinical research and explains the major factors that influence its determination. Examples from different study settings, including superiority, non-inferiority, and bioequivalence studies, are used to bridge statistical concepts with practical application. Common misconceptions surrounding sample size are also discussed to improve understanding among clinical research professionals.