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Target and actual sample sizes for studies from two trial registries from 1999 to 2020: an observational study

OBJECTIVES: To investigate differences between target and actual sample sizes, and what study characteristics were associated with sample sizes. DESIGN: Observational study. SETTING: The large trial registries of clinicaltrials.gov (starting in 1999) and ANZCTR (starting in 2005) through to 2021. PA...

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Autores principales: Barnett, Adrian Gerard, Glasziou, Paul
Formato: Online Artículo Texto
Lenguaje:English
Publicado: BMJ Publishing Group 2021
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8719224/
http://dx.doi.org/10.1136/bmjopen-2021-053377
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author Barnett, Adrian Gerard
Glasziou, Paul
author_facet Barnett, Adrian Gerard
Glasziou, Paul
author_sort Barnett, Adrian Gerard
collection PubMed
description OBJECTIVES: To investigate differences between target and actual sample sizes, and what study characteristics were associated with sample sizes. DESIGN: Observational study. SETTING: The large trial registries of clinicaltrials.gov (starting in 1999) and ANZCTR (starting in 2005) through to 2021. PARTICIPANTS: Over 280 000 interventional studies excluding studies that were withheld, terminated for safety reasons or were expanded access. MAIN OUTCOME MEASURES: The actual and target sample sizes, and the within-study ratio of the actual to target sample size. RESULTS: Most studies were small: the median actual sample sizes in the two databases were 60 and 52. There was a decrease over time in the target sample size of 9%–10% per 5 years, and a larger decrease of 18%–21% per 5 years for the actual sample size. The actual-to-target sample size ratio was 4.1% lower per 5 years, meaning more studies (on average) failed to hit their target sample size. CONCLUSION: Registered studies are more often under-recruited than over-recruited and worryingly both target and actual sample sizes appear to have decreased over time, as has the within-study gap between the target and actual sample size. Declining sample sizes and ongoing concerns about underpowered studies mean more research is needed into barriers and facilitators for improving recruitment and accessing data.
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spelling pubmed-87192242022-01-12 Target and actual sample sizes for studies from two trial registries from 1999 to 2020: an observational study Barnett, Adrian Gerard Glasziou, Paul BMJ Open Evidence Based Practice OBJECTIVES: To investigate differences between target and actual sample sizes, and what study characteristics were associated with sample sizes. DESIGN: Observational study. SETTING: The large trial registries of clinicaltrials.gov (starting in 1999) and ANZCTR (starting in 2005) through to 2021. PARTICIPANTS: Over 280 000 interventional studies excluding studies that were withheld, terminated for safety reasons or were expanded access. MAIN OUTCOME MEASURES: The actual and target sample sizes, and the within-study ratio of the actual to target sample size. RESULTS: Most studies were small: the median actual sample sizes in the two databases were 60 and 52. There was a decrease over time in the target sample size of 9%–10% per 5 years, and a larger decrease of 18%–21% per 5 years for the actual sample size. The actual-to-target sample size ratio was 4.1% lower per 5 years, meaning more studies (on average) failed to hit their target sample size. CONCLUSION: Registered studies are more often under-recruited than over-recruited and worryingly both target and actual sample sizes appear to have decreased over time, as has the within-study gap between the target and actual sample size. Declining sample sizes and ongoing concerns about underpowered studies mean more research is needed into barriers and facilitators for improving recruitment and accessing data. BMJ Publishing Group 2021-12-24 /pmc/articles/PMC8719224/ http://dx.doi.org/10.1136/bmjopen-2021-053377 Text en © Author(s) (or their employer(s)) 2021. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ. https://creativecommons.org/licenses/by-nc/4.0/This is an open access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited, appropriate credit is given, any changes made indicated, and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/ (https://creativecommons.org/licenses/by-nc/4.0/) .
spellingShingle Evidence Based Practice
Barnett, Adrian Gerard
Glasziou, Paul
Target and actual sample sizes for studies from two trial registries from 1999 to 2020: an observational study
title Target and actual sample sizes for studies from two trial registries from 1999 to 2020: an observational study
title_full Target and actual sample sizes for studies from two trial registries from 1999 to 2020: an observational study
title_fullStr Target and actual sample sizes for studies from two trial registries from 1999 to 2020: an observational study
title_full_unstemmed Target and actual sample sizes for studies from two trial registries from 1999 to 2020: an observational study
title_short Target and actual sample sizes for studies from two trial registries from 1999 to 2020: an observational study
title_sort target and actual sample sizes for studies from two trial registries from 1999 to 2020: an observational study
topic Evidence Based Practice
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8719224/
http://dx.doi.org/10.1136/bmjopen-2021-053377
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