Sample Size and Statistical Power
Pre-trial calculation of the number of subjects needed to detect a specified treatment effect with acceptable Type I and Type II error rates.
Definition
Sample size and power calculations determine how many subjects a clinical trial must enroll to detect a pre-specified effect size with acceptable false-positive (Type I error, alpha, typically 0.05 two-sided) and false-negative (Type II error, beta, typically 0.20, i.e., 80% power) rates. Inputs include the expected effect size, the variance of the outcome, the test statistic, allocation ratio, and any planned interim analyses. Under-powered trials are a leading cause of inconclusive pivotal studies.What this means in practice
MedTech pivotal trials commonly target 80-90% power for the primary endpoint. Adaptive designs and Bayesian designs allow for sample-size re-estimation under pre-specified rules.- •Powering only the primary endpoint and finding the trial cannot answer key secondary endpoints used for label or HEOR.
- •Optimistic effect-size assumptions that produce a too-small sample size.
Related terms
Grouped by themeEditor's picks
· Hand-selected related conceptsTrial design that pre-specifies opportunities to modify aspects (sample size, arms, endpoints) based on interim data.
Trial design that uses Bayesian statistics, often incorporating prior data from related studies or registries.
International standard for the design, conduct, and reporting of clinical trials.
Definitive clinical study designed to establish safety and effectiveness for marketing authorization.
More in Clinical & Trials
· Same categoryThe pre-specified outcomes that determine trial success (primary), provide supporting evidence (secondary), or generate hypotheses (exploratory).
Any untoward medical occurrence in a subject, whether or not related to the device.
Data integrity principles: Attributable, Legible, Contemporaneous, Original, Accurate (plus Complete, Consistent, Enduring, Available).
An IVD's ability to detect small quantities of an analyte.
Primary references
3 sources- 1
ICH E9 Statistical PrinciplesVerifiedICHich.org
- 2
FDA Guidance, Adaptive Designs for Clinical Trials (2019)VerifiedFDAfda.gov
- 3
ClinicalTrials.govVerifiedNIHclinicaltrials.gov
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