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Randomized controlled trials: who fails run-in?


Early identification of enrollees at risk of poor adherence and run-in failure (RIF) may present opportunities to increase trial efficiency and generalizability.


We conducted a factorial-design randomized, controlled trial of calcium and vitamin D to prevent colorectal adenoma recurrence. At the enrolment interview, study coordinators at 11 centers collected demographic and medical information and participants’ beliefs about the study tablets. Participants also completed two self-administered questionnaires (SAQ) before a three-month single-blinded placebo run-in. Eligible participants were then randomized to calcium, vitamin D, both or neither; women electing to take calcium were randomized to vitamin D or placebo. A priori, we considered three subgroups: men (N=1606) and women (N=301) in the full factorial randomization and women in the 2-arm randomization (N=666).


Overall, 314 of 2,573 (12%) enrollees potentially eligible for randomization failed run-in due to poor adherence (took <80% tablets) or refusal to participate. In multivariable models in the largest subgroup (males), RIF was associated with younger age (adjusted odds ratio per 5 years 0.85; 95% CI 0.76-0.96), single marital status (1.67; 1.12-2.49), any missing data on the SAQs (2.05; 1.46-2.86) study center (p<0.0001) and perceived toxicity report (12.86; 5.41-30.56). Across all three subgroups, the latter three factors were most consistently associated with RIF but other factors are described which vary by subgroup.


The most consistent predictors of RIF were perceived toxicities, missing data on self-administered questionnaires, and study center. The latter two findings relate to study coordinator oversight, and present potential opportunities to improve adherence during run-in.

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This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The Creative Commons Public Domain Dedication waiver ( applies to the data made available in this article, unless otherwise stated.

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Rees, J.R., Mott, L.A., Barry, E.L. et al. Randomized controlled trials: who fails run-in?. Trials 16 (Suppl 2), O78 (2015).

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