Recruitment patterns in multicentre randomised trials fit more closely to Price's Law than the Pareto Principle: A review of trials funded and published by the United Kingdom Health Technology Assessment Programme

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This review investigates whether the distribution of recruitment to multicentre randomised controlled trials (RCTs) fits the “Pareto Principle”, i.e. 80% of participants are recruited by 20% of sites, or Price's Law, i.e. 50% of participants are recruited by the square root of the total number of sites.

A review of HTA reports published between 2017 and 2019.

40 RCTs conducted face-to-face recruitment, five recruited via mail-outs and one used both methods. For face-to-face recruitment (n = 41 studies), 80% of participants were recruited by the top recruiting 42.6% of sites; for mail-out methods (n = 6 studies) this was 52.0%. From the square root of sites, 51.3% and 31.8% of participants were recruited for the two recruitment approaches, respectively. Specifically, 3 (7.3%, 95% CI 2.5% to 19.4%) and 20 (48.8%, 95% CI 34.3% to 63.5%) RCTs that recruited face-to-face followed Pareto Principle and Price's Law, respectively. One mail-out recruitment study followed one of these principles, Price's Law. Chief Investigator (CI) sites (n = 24) in face-to-face recruitment studies recruited 18.1% of participants.

Face-to-face recruitment to HTA-funded RCTs fits more closely to Price's Law than the Pareto Principle, with the CI's site recruiting nearly a fifth of participants. Since we focussed on HTA-funded RCTs with ≥9 recruiting sites and for which the recruitment method and number recruited by site were known, our findings are limited in their generalisability. However, this trend could be used as a guide to aid in estimating how many sites RCTs need. More accurate estimation may prevent the need for recruitment extensions.
Original languageEnglish
Article number106665
Number of pages10
JournalContemporary Clinical Trials
Early online date27 Dec 2021
Publication statusPublished - 1 Feb 2022

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