Power calculators
Calculate how big your clinical trial needs to be with our easy to use online calculators.
There are three different calculators below - choose the correct one according to the type of trial you are planning (superiority/equivalence) and the nature of the primary outcome variable (qualitative/quantitive). A superiority trial is one where you want to demonstrate that one treatment or intervention is better than another (or better than no treatment/intervention). An equivalence trial is where you want to demonstrate that one treatment is no better or worse than an existing treatment.
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Qualitative superiority trial
A qualitative outcome is one that can be described by categories, such as dead/alive, hospitalisation - yes/no, therapeutic success/failure and so on. This calculator is designed for binary outcomes in parallel group superiority trials. The percentage of patients that meet the primary outcome definition (e.g. percentage hospitalised) is compared between two randomised groups. You should power the trial to be able to detect the smallest clinically important difference between these percentages.
Technical note
Calculation based on the formula: n = f(α, β) × [p1 × (100 − p1) +
p2 × (100 − p2)] / (p2 − p1)2
where f(α, β) = [Φ-1(α/2) + Φ-1(β)]2,
Φ-1 being the cumulative distribution function of a standardised normal deviate
(reference: Pocock SJ. Clinical Trials: A Practical Approach. Wiley; 1983).