Rationale for unequal randomization in clinical trials is rarely reported: a systematic review

Abstract

Objectives: To assess the reporting of the unequal randomization ratio in reports of trials with this design and to identify the justification for the design.

Study design and setting: Systematic review of reports of trials with unequal randomization. We selected all original reports of two parallel-group randomized controlled trials with unequal randomization, which were published in 2009 and 2010 in core clinical journals in MEDLINE on the basis of the abstract (and full text, if necessary). Additional information was collected by an author survey.

Results: We retrieved 106 reports (prevalence, 4.7%). The randomization ratio was not stated in 8.5% of reports and 51.9% of abstracts. Sample size calculation was reported in 70 reports, with unequal randomization not taken into account in 25.7% (n = 18). Justification for unequal randomization was not reported in 77.4% (n = 82) of reports. Combining information from reports and author surveys, we had justification for 41 trials. The main justification was safety issues for 20 trials. In 11 of those latter 20 reports, adverse events were not fully reported.

Conclusion: A better reporting of the randomization ratio, sample size calculation, and justification to unequal randomization could help readers appraise the quality and risk of bias of such trials.

Keywords: Justification; Randomization ratio; Randomized controlled trials; Reporting; Systematic review; Unequal randomization.