--- title: "Sample Size and Statistical Power… | MedTech Terms" description: "Pre-trial calculation of the number of subjects needed to detect a specified treatment effect with acceptable Type I and Type II error rates." lang: en json-ld: | { "@context": "https://schema.org", "@graph": [ { "@type": "DefinedTerm", "@id": "https://medtechterms.com/terms/sample-size-power#term", "name": "Sample Size and Statistical Power", "alternateName": [ "Power calculation", "Sample size justification" ], "description": "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. 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[Home](/) 2. / 3. [Terms](/terms) 4. / 5. [Clinical & Trials](/terms?cat=Clinical%20%26%20Trials) 6. / 7. Sample Size and Statistical Power [All terms](/terms) Clinical & Trials [Clinical Evidence](/ecosystems/clinical-evidence) # 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. Reviewed by [Christian Espinosa, Founder, Blue Goat Cyber](/authors/christian-espinosa) Last reviewed May 9, 2026 ## 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 the regulation says FDA Guidance: 'Statistical Guidance on Reporting Results from Studies Evaluating Diagnostic Tests' and ICH E9 'Statistical Principles for Clinical Trials' both require pre-specified sample-size justification in the protocol. ## What this means in practice MedTech pivotal trials commonly target 80-90% power for the [primary endpoint](/terms/primary-secondary-endpoint). Adaptive designs and Bayesian designs allow for sample-size re-estimation under pre-specified rules. Common pitfalls - • 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 theme ### Editor's picks · Hand-selected related concepts [ Clinical & Trials Adaptive Trial Design Trial design that pre-specifies opportunities to modify aspects (sample size, arms, endpoints) based on interim data. ](/terms/adaptive-trial)[ Clinical & Trials Bayesian Trial Design Trial design that uses Bayesian statistics, often incorporating prior data from related studies or registries. ](/terms/bayesian-trial)[ Clinical & Trials ICH E6 Good Clinical Practice(GCP) International standard for the design, conduct, and reporting of clinical trials. ](/terms/ich-gcp)[ Clinical & Trials Pivotal Trial Definitive clinical study designed to establish safety and effectiveness for marketing authorization. ](/terms/pivotal-trial) ### More in Clinical & Trials · Same category [ Clinical & Trials Primary and Secondary Endpoints The pre-specified outcomes that determine trial success (primary), provide supporting evidence (secondary), or generate hypotheses (exploratory). ](/terms/primary-secondary-endpoint)[ Clinical & Trials Adverse Event(AE) Any untoward medical occurrence in a subject, whether or not related to the device. ](/terms/adverse-event)[ Clinical & Trials ALCOA+ Data integrity principles: Attributable, Legible, Contemporaneous, Original, Accurate (plus Complete, Consistent, Enduring, Available). ](/terms/alcoa-plus)[ Clinical & Trials Analytical Sensitivity An IVD's ability to detect small quantities of an analyte. ](/terms/analytical-sensitivity) Cited by Where this term appears across MedTech Terms. Ecosystems (1) - [Clinical Evidence](/ecosystems/clinical-evidence) ## Primary references 3 sources Link health: 3 verified · last checked 2026-06-20 ICH· 1 FDA· 1 NIH· 1 1. [1 ICH E9 Statistical Principles Verified ICH · ich.org ](https://www.ich.org/page/efficacy-guidelines) 2. [2 FDA Guidance, Adaptive Designs for Clinical Trials (2019) Verified FDA · fda.gov ](https://www.fda.gov/regulatory-information/search-fda-guidance-documents/adaptive-design-clinical-trials-drugs-and-biologics-guidance-industry) 3. [3 ClinicalTrials.gov Verified NIH · clinicaltrials.gov ](https://clinicaltrials.gov/) Inline markers like \[1\] jump to the matching reference above. Sponsor note ### Clinical evidence intersecting with device security? We support clinical-stage MedTech teams whose investigational devices touch patient data or hospital networks. [Book a 30-minute discovery session](https://go.bluegoatcyber.com/meetings/blue-goat-cyber/discovery-session) - No obligation - Expert-led from minute one - NDA available on request MedTech Terms is a community resource sponsored by [Blue Goat Cyber](https://bluegoatcyber.com). Definitions are independent of any vendor. On this term Category Clinical & Trials Sources 3 Updated 5/9/2026 [Compare with another term](/compare?a=sample-size-power) Learn in 60 seconds Card Lesson Quiz Pre-trial calculation of the number of subjects needed to detect a specified treatment effect with acceptable Type I and Type II error rates. - · 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. - · Inputs include the expected effect size, the variance of the outcome, the test statistic, allocation ratio, and any planned interim analyses. Remember this Watch out: Powering only the primary endpoint and finding the trial cannot answer key secondary endpoints used for label or HEOR. Related terms - [Pivotal Trial ](/terms/pivotal-trial) - [Adaptive Trial Design ](/terms/adaptive-trial) - [Bayesian Trial Design ](/terms/bayesian-trial) - [ICH E6 Good Clinical Practice(GCP) ](/terms/ich-gcp) - [Primary and Secondary Endpoints ](/terms/primary-secondary-endpoint) You may also need Auto-suggested from Clinical & Trials and shared keywords. - [Lost to Follow-up ](/terms/lost-to-followup) - [Composite Endpoint ](/terms/composite-endpoint) - [Real-World Data(RWD) ](/terms/rwd) - [Feasibility Study ](/terms/feasibility-study) - [Master Protocol (Basket / Umbrella / Platform) ](/terms/master-protocol) - [Blinding and Masking ](/terms/blinding) [All Clinical & Trials terms](/terms?cat=Clinical%20%26%20Trials) From the Blue Goat network Related resources and services on this topic. - [ MedTech Launchpad MedTech funding rounds, accelerators, and launch resources. ](https://medtechlaunchguide.com) MedTech Terms An authoritative, plain-language reference for the regulatory, quality, cybersecurity, and software terms that shape modern medical devices. 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