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The number needed to treat is an estimate of how many people need to receive a treatment before one person would experience a good outcome. It is used as a measure of the absolute effectiveness of treatments.
For example, if a study found that for every 100 participants allocated to a drug there was one less death over a period of one year compared to every 100 people allocated to a placebo, the number needed to treat would be 100 for one year.
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