{ "id": "epp507afce", "slug": "mega-trial", "title": "Mega-trial", "updated": "2026-10-15", "topic_path": [ { "id": "life", "label": "Life and health", "api_url": "https://www.edgepedia.org/api/v1/topics/life" }, { "id": "life.health", "label": "Human health and medicine", "api_url": "https://www.edgepedia.org/api/v1/topics/life.health" }, { "id": "life.health.public", "label": "Public health and healthcare", "api_url": "https://www.edgepedia.org/api/v1/topics/life.health.public" }, { "id": "life.health.public.clinical-research-trials", "label": "Clinical research and trials", "api_url": "https://www.edgepedia.org/api/v1/topics/life.health.public.clinical-research-trials" } ], "geo": [ { "id": "geo.nongeo.t1946.life.health.public.clinical-research-trials", "label": "Non-geographic · 1946 to 2000: Clinical research and trials", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo.t1946.life.health.public.clinical-research-trials", "path": [ { "id": "geo.nongeo", "label": "Non-geographic", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo" }, { "id": "geo.nongeo.t1946", "label": "Non-geographic · 1946 to 2000", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo.t1946" }, { "id": "geo.nongeo.t1946.life", "label": "Life and health", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo.t1946.life" }, { "id": "geo.nongeo.t1946.life.health", "label": "Human health and medicine", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo.t1946.life.health" }, { "id": "geo.nongeo.t1946.life.health.public", "label": "Public health and healthcare", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo.t1946.life.health.public" }, { "id": "geo.nongeo.t1946.life.health.public.clinical-research-trials", "label": "Clinical research and trials", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo.t1946.life.health.public.clinical-research-trials" } ] } ], "excerpt": "A mega-trial is a very large randomized controlled trial, usually enrolling many thousands of patients across many centers, designed to detect modest treatment effects such as 15–20% reductions in death.", "snippet": "A mega-trial is a very large randomized controlled trial, usually enrolling many thousands of patients across many centers, designed to detect modest treatment effects such as 15–20% reductions in death.", "node": "life.health.public.clinical-research-trials", "markdown": "# Mega-trial\n\nA mega-trial is a very large randomized controlled trial, usually enrolling many thousands of patients across many centers, designed to detect modest treatment effects on major clinical outcomes such as mortality. A working definition from the meta-research literature sets the threshold at more than 10,000 participants[1](https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2823295), and the design is characterized by highly inclusive recruitment criteria, maximally simplified protocols, and unambiguous endpoints such as mortality.[2](https://pmc.ncbi.nlm.nih.gov/articles/PMC59645/) Mega-trials exist because the treatment effects worth detecting in medicine, often 15–20% relative reductions in death, are too small for trials of a few thousand patients to measure reliably.[3](https://onlinelibrary.wiley.com/doi/10.1002/sim.4780030421)\n\n| Key fact | Detail |\n|---|---|\n| Working size threshold | More than 10,000 participants[1](https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2823295) |\n| Endpoints needed | Roughly 1,000–2,000 endpoints to assess a 15–20% mortality reduction, typically 10,000–20,000 good-prognosis patients[3](https://onlinelibrary.wiley.com/doi/10.1002/sim.4780030421) |\n| Canonical example | ISIS-2: 17,187 patients, 417 hospitals, 16 countries, published 1988[4](https://pubmed.ncbi.nlm.nih.gov/2899772/) |\n| Cost control | Streamlining can cut costs by more than 90%; RECOVERY cost under £40 per patient per answer[5](https://08a59754f7.nxcli.net/wp-content/uploads/2021/07/CTTI_Large_Simple_Trials_Meeting_Regulatory_Ops_Kweder.pdf) • [6](https://link.springer.com/article/10.1186/s13063-025-08724-x) |\n| Scale of evidence | 120 mega-trials identified in a systematic review; 41 showed a significant primary-outcome result[1](https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2823295) |\n| Fields with examples | Cardiology (ISIS series, GISSI-I, GUSTO-I) and stroke (IST)[7](https://www.annals.edu.sg/megatrials-of-drug-treatments-strengths-and-limitations/) |\n\n## How it works\n\nThe statistical logic is driven by event counts. Reliable assessment of a moderate 15–20% mortality reduction generally requires not one or two thousand patients but one to two thousand endpoints, which means randomizing some 10,000 or 20,000 patients with a good prognosis, or several thousand with a poor prognosis.[3](https://onlinelibrary.wiley.com/doi/10.1002/sim.4780030421) Sample size is inversely proportional to the square of the declared absolute treatment difference: detecting a 1.2% absolute difference requires about 10,900 patients, 2.4% about 2,400, and 0.6% about 46,300.[8](https://www.mcgill.ca/gimprogram/files/gimprogram/part_3_rct_design_jacc_2015.pdf) Equivalently, detecting a hazard ratio (statistical measure of how quickly one group experiences events) of 0.85 (a 15% relative risk reduction) with 80% power requires 1,194 primary events, against 252 events for a hazard ratio of 0.70; because power depends mainly on the number of patients experiencing the primary event, some trials are event-driven.[8](https://www.mcgill.ca/gimprogram/files/gimprogram/part_3_rct_design_jacc_2015.pdf)\n\nThe motivation is that small trials systematically miss modest effects: 21 of 24 trials of long-term beta blockade after myocardial infarction were individually too small to detect the 22% relative risk reduction that later meta-analysis established.[9](https://media.tghn.org/articles/trialprotocoltool_sp/SOURCE/Extras/Stats/DLSLargeTrials.pdf) Randomization followed by analysis by allocated rather than actual treatment (intention to treat) controls systematic error, while random error is minimized only by very large size.[3](https://onlinelibrary.wiley.com/doi/10.1002/sim.4780030421)\n\n## How it is done\n\nMega-trials achieve their size by stripping the protocol to essentials. ISIS-1 randomized patients by a 2-minute telephone call to a centralized 24-hour service in over 250 centers in 14 countries, with no entry form; entry data such as heart rate, blood pressure, age, sex, and diabetes were collected by telephone, and over 16,000 patients were enrolled by the end of 1984 at a cost of about two million US dollars.[3](https://onlinelibrary.wiley.com/doi/10.1002/sim.4780030421) ISIS-2 used a 2×2 factorial design with entry by a single telephone call, no restriction on ancillary treatments, and follow-up after discharge limited to mortality through government records wherever possible.[10](https://www.jameslindlibrary.org/wp-data/uploads/2014/07/ISIS-2_Collaborative_Group_1988.pdf)\n\nOther simplifications follow the same logic. Entry criteria are kept as wide and simple as possible; treatment compliance needs only crude measurement by patient reporting or pill counting; and cause-specific mortality can be obtained from centralized government archives in countries such as the UK, Sweden, Norway, Denmark, Finland, the US, and Canada at nominal cost.[3](https://onlinelibrary.wiley.com/doi/10.1002/sim.4780030421) Follow-up in ISIS-2 was 99% complete to discharge, 97% to week 5, and 96% to January 1, 1988.[10](https://www.jameslindlibrary.org/wp-data/uploads/2014/07/ISIS-2_Collaborative_Group_1988.pdf) By some estimates a streamlined approach reduces costs by more than 90%.[5](https://08a59754f7.nxcli.net/wp-content/uploads/2021/07/CTTI_Large_Simple_Trials_Meeting_Regulatory_Ops_Kweder.pdf) Some trials run without external funding altogether: CREATE was initiated in 2000 by investigators from Canada, China, and India using internal funds from the Population Health Research Institute at [McMaster University](https://www.edgepedia.org/mcmaster-university).[11](https://pmc.ncbi.nlm.nih.gov/articles/PMC7118878/)\n\n## Origin\n\nThe design rationale was set out in the paper \"Why do we need some large, simple randomized trials?\" by [Salim Yusuf](https://www.edgepedia.org/salim-yusuf), Rory Collins, and [Richard Peto](https://www.edgepedia.org/richard-peto), published in *Statistics in Medicine* in 1984.[3](https://onlinelibrary.wiley.com/doi/10.1002/sim.4780030421) Earlier work the method built on includes the 1954 Salk polio vaccine trial, which recruited over 600,000 US schoolchildren.[9](https://media.tghn.org/articles/trialprotocoltool_sp/SOURCE/Extras/Stats/DLSLargeTrials.pdf) The Oxford program then produced the ISIS series: ISIS-2 (published in *The Lancet* on August 13, 1988), ISIS-3 (41,299 patients, 3×2 factorial), and ISIS-4 (58,050 patients, 2×2×2 factorial).[12](https://www.thelancet.com/journals/lancet/article/PIIS0140-6736%2815%2961505-7/fulltext) Other early trials recruiting more than 10,000 patients include GISSI-1, the International Stroke Trial (19,435 patients), and GUSTO-I[7](https://www.annals.edu.sg/megatrials-of-drug-treatments-strengths-and-limitations/); GISSI-2 randomized 12,490 patients in a factorial comparison of alteplase versus streptokinase and heparin versus no heparin.[13](https://nyaspubs.onlinelibrary.wiley.com/doi/10.1111/j.1749-6632.1993.tb26369.x)\n\n## Variants\n\nThe umbrella term large simple trial covers several modern forms: platform trials such as RECOVERY, registry trials such as TASTE, and nested trials.[6](https://link.springer.com/article/10.1186/s13063-025-08724-x) TASTE was the first medical-device registry-based randomized trial, using the SWEDEHEART registry for screening, randomization, and follow-up, and obtaining its all-cause mortality endpoint by direct linkage with the Swedish Population Registry.[6](https://link.springer.com/article/10.1186/s13063-025-08724-x) \"Pragmatic\" refers to mimicking routine practice, while \"large\" is what provides precision against random error; broad inclusion supports external validity while large cohorts give precise internal estimates.[6](https://link.springer.com/article/10.1186/s13063-025-08724-x) Nested designs also exist: Mega-ROX Sepsis runs inside a 40,000-patient registry-embedded trial of conservative versus liberal ICU oxygenation.[14](https://discovery.ucl.ac.uk/id/eprint/10173831/1/1-s2.0-S1441277223000108-main.pdf)\n\n## Applications\n\nCardiology dominates. ISIS-2 showed streptokinase reduced 5-week vascular mortality from 12.0% to 9.2% (odds reduction 25%, SD 4) and aspirin from 11.8% to 9.4% (odds reduction 23%, SD 4), while the combination reduced mortality to 8.0% versus 13.2% for neither (odds reduction 42%, SD 5; 95% CI 34–50%).[4](https://pubmed.ncbi.nlm.nih.gov/2899772/) The benefit persisted: streptokinase allocation was associated with 29 fewer deaths per 1,000 patients during days 0–35 and 23 fewer per 1,000 at 10 years.[15](https://pmc.ncbi.nlm.nih.gov/articles/PMC28530/) Practice changed quickly: routine streptokinase use in UK acute myocardial infarction grew from 2–3% in 1987 to 68% in 1989.[12](https://www.thelancet.com/journals/lancet/article/PIIS0140-6736%2815%2961505-7/fulltext) ISIS-4 concluded that magnesium was worthless in acute myocardial infarction, refuting a meta-analysis of smaller trials suggesting benefit.[9](https://media.tghn.org/articles/trialprotocoltool_sp/SOURCE/Extras/Stats/DLSLargeTrials.pdf) HOPE showed ramipril produced a 22% relative risk reduction for MI, stroke, or cardiovascular death, while vitamin E was not effective.[9](https://media.tghn.org/articles/trialprotocoltool_sp/SOURCE/Extras/Stats/DLSLargeTrials.pdf) Outside cardiology, VITAL enrolled 25,000 healthy older individuals by mail in a 2×2 factorial design powered to detect 10–15% reductions in primary outcomes[16](https://www.ncbi.nlm.nih.gov/books/NBK201272/), and stroke is represented by the International Stroke Trial.[7](https://www.annals.edu.sg/megatrials-of-drug-treatments-strengths-and-limitations/)\n\n## Limitations and alternatives\n\nThe design's hallmark, deliberate reduction of experimental control to maximize recruitment, is also its fundamental methodological deficiency.[2](https://pmc.ncbi.nlm.nih.gov/articles/PMC59645/) Analysis is only meaningful at the group level, and mega-trials can be repeated but not replicated.[17](https://www.sciencedirect.com/science/article/pii/S0035881925006233) Premature mega-trials run without prior knowledge of a drug tend systematically to underestimate its effect size.[2](https://pmc.ncbi.nlm.nih.gov/articles/PMC59645/) Funding is a further constraint, often restricted to industry sources[18](https://journals.plos.org/plosmedicine/article?id=10.1371%2Fjournal.pmed.0050004), and single trials, even very large ones, seldom provide definitive answers.[18](https://journals.plos.org/plosmedicine/article?id=10.1371%2Fjournal.pmed.0050004)\n\nAgainst meta-analysis, the comparison is close but not identical. A systematic review found no difference between mega-trials and meta-analyses of smaller trials for primary outcomes or all-cause mortality (ROR 1.00; 95% CI 0.97–1.04), but smaller trials published before the mega-trials gave more favorable results (ROR 1.05; 95% CI 1.01–1.10).[1](https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2823295) Earlier estimates put meta-analysis–megatrial disagreement at roughly 35% or between 10% and 23%, and megatrials sometimes disagree with each other by as much as meta-analyses disagree with megatrials.[19](https://mentalhealth.bmj.com/content/7/2/34) A large poorly controlled trial can have a confidence interval similar to a small well-controlled one without the studies being equivalent.[2](https://pmc.ncbi.nlm.nih.gov/articles/PMC59645/) ISIS-2's famous astrological (birth-sign) subgroup analysis, added during peer review, remains the standard illustration of why subgroup claims from any single trial deserve caution.[12](https://www.thelancet.com/journals/lancet/article/PIIS0140-6736%2815%2961505-7/fulltext)\n\n## References\n\n1. [Agreement Between Mega-Trials and Smaller Trials: A Systematic Review and Meta-Research Analysis (JAMA Network Open)](https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2823295)\n2. [Fundamental deficiencies in the megatrial methodology (Charlton)](https://pmc.ncbi.nlm.nih.gov/articles/PMC59645/)\n3. [Why do we need some large, simple randomized trials? (Statistics in Medicine, 1984)](https://onlinelibrary.wiley.com/doi/10.1002/sim.4780030421)\n4. [Randomised trial of intravenous streptokinase, oral aspirin, both, or neither among 17,187 cases of suspected acute myocardial infarction: ISIS-2 (Lancet 1988)](https://pubmed.ncbi.nlm.nih.gov/2899772/)\n5. [Opportunities for Large Simple Trials – An FDA Perspective (Kweder, CTTI, 2013)](https://08a59754f7.nxcli.net/wp-content/uploads/2021/07/CTTI_Large_Simple_Trials_Meeting_Regulatory_Ops_Kweder.pdf)\n6. [Large simple randomized controlled trials, from drugs to medical devices: lessons from recent experience (Trials, 2025)](https://link.springer.com/article/10.1186/s13063-025-08724-x)\n7. [Megatrials of Drug Treatments: Strengths and Limitations (Annals, Academy of Medicine, Singapore)](https://www.annals.edu.sg/megatrials-of-drug-treatments-strengths-and-limitations/)\n8. [Design of Major Randomized Trials (JACC)](https://www.mcgill.ca/gimprogram/files/gimprogram/part_3_rct_design_jacc_2015.pdf)\n9. [Large, Simple Trials (Sackett, Clinical Epidemiology 3rd ed., 2004)](https://media.tghn.org/articles/trialprotocoltool_sp/SOURCE/Extras/Stats/DLSLargeTrials.pdf)\n10. [ISIS-2 full trial report (Lancet 1988) via James Lind Library](https://www.jameslindlibrary.org/wp-data/uploads/2014/07/ISIS-2_Collaborative_Group_1988.pdf)\n11. [Challenges in the conduct of large simple trials... CREATE and ECLA trial program (PMC)](https://pmc.ncbi.nlm.nih.gov/articles/PMC7118878/)\n12. [The social history of ISIS-2: triumph and the path not taken - The Lancet](https://www.thelancet.com/journals/lancet/article/PIIS0140-6736%2815%2961505-7/fulltext)\n13. [Large-Scale Randomized Evidence: Large, Simple Trials and Overviews of Trials (Annals NY Acad Sci, 1993)](https://nyaspubs.onlinelibrary.wiley.com/doi/10.1111/j.1749-6632.1993.tb26369.x)\n14. [Protocol and statistical analysis plan for Mega-ROX Sepsis (2023)](https://discovery.ucl.ac.uk/id/eprint/10173831/1/1-s2.0-S1441277223000108-main.pdf)\n15. [ISIS-2: 10 year survival among patients with suspected acute myocardial infarction (BMJ)](https://pmc.ncbi.nlm.nih.gov/articles/PMC28530/)\n16. [Examples of Large Simple Trials (NCBI Bookshelf, IOM discussion)](https://www.ncbi.nlm.nih.gov/books/NBK201272/)\n17. [Mega-Trials: Methodological Issues and Clinical Implications (J R Coll Physicians Lond, 1995, Charlton)](https://www.sciencedirect.com/science/article/pii/S0035881925006233)\n18. [In the Era of Systematic Reviews, Does the Size of an Individual Trial Still Matter? (PLOS Medicine)](https://journals.plos.org/plosmedicine/article?id=10.1371%2Fjournal.pmed.0050004)\n19. [Meta-analyses and megatrials: neither is the infallible, universal standard (BMJ Mental Health)](https://mentalhealth.bmj.com/content/7/2/34)\n\n---\n*Topic: Encyclopedia › Life and health › Human health and medicine › Public health and healthcare › Clinical research and trials*\n\n*Initially written Sep 29, 2026 · Edited: Oct 15, 2026*\n\n*Copyright 2026 EdgeChat AI, a subsidiary of Biostate AI.*\n\nLicense: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license\n", "same_as": [], "url": "https://www.edgepedia.org/mega-trial", "markdown_url": "https://www.edgepedia.org/mega-trial.md", "license": { "name": "Edgepedia Community License 1.0", "url": "https://www.edgepedia.org/edgepedia/license", "summary": "Free with credit, commercial use included. AI training is open to everyone. For other uses, organizations over USD 100M in revenue or 100M monthly users license separately.", "spdx": "LicenseRef-Edgepedia-Community-1.0" }, "credit": "\"Mega-trial\", Edgepedia (EdgeChat), https://www.edgepedia.org/mega-trial. Edgepedia Community License 1.0.", "credit_md": "\"[Mega-trial](https://www.edgepedia.org/mega-trial)\", Edgepedia (EdgeChat), [https://www.edgepedia.org/mega-trial](https://www.edgepedia.org/mega-trial). [Edgepedia Community License 1.0](https://www.edgepedia.org/edgepedia/license).", "credit_html": "\"Mega-trial\", Edgepedia (EdgeChat), https://www.edgepedia.org/mega-trial. Edgepedia Community License 1.0.", "speakable": "A mega-trial is a very large randomized controlled trial, usually enrolling many thousands of patients across many centers, designed to detect modest treatment effects such as 15–20% reductions in death." }