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sample size

— The actual or intended number of participants in a study

Full explanation:

The intended sample size of a study is the estimated number of participants required to yield differences in outcomes of a specified degree of confidence.

This estimate is usually made by calculating statistical power. The sample size should be adequate to provide a high probability of detecting "statistically significant" differences of a given magnitude between treatment effects, if such an effect actually exists.

The achieved sample size is the number of participants enrolled, treated or analysed in a study.

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