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Statistical power calculator
Enter the sample size you can realistically recruit and the effect you expect. You get the power of that design — and an honest reading of what a non-significant result would tell you if power is low.
If a design has 40% power, failing to find an effect tells you almost nothing — the effect might be absent, or simply undetectable. That is worth knowing before data collection, not after.
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This calculator was checked by Sidra Khan, Lead Biostatistician
In short
What is statistical power?
Statistical power is the probability that a study will detect an effect of a given size, if that effect genuinely exists. A study powered at 80% has a one in five chance of missing a real effect. Power increases with sample size and with the size of the effect being detected.
Further reading
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