Sample Size — What It Means in Clinical Trials
Plain English Definition
Sample size is the number of participants needed in a trial to detect a meaningful treatment effect. Statisticians calculate the ideal sample size before the trial starts, based on how large they expect the effect to be. Larger trials can detect smaller differences between treatments, but they take longer and cost more.
Why It Matters
A trial with too few participants may miss a real treatment effect. When looking at trial results, consider the sample size — results from a 50-person trial are less reliable than results from a 5,000-person trial.
Example
A listing might say: "Target enrollment: 1,200 participants across 80 sites worldwide." This is the calculated sample size needed to answer the trial's primary question.
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