Objectives To describe and summarise how the results of randomised controlled trials (RCTs) that did not find a significant treatment effect are reported, and to estimate how commonly trial reports make unwarranted claims.
Design We performed a retrospective survey of published RCTs, published in four high impact factor general medical journals between June 2016 and June 2017.
Setting Trials conducted in all settings were included.
Participants 94 reports of RCTs that did not find a difference in their main comparison or comparisons were included.
Interventions All interventions.
Primary and secondary outcomes We recorded the way the results of each trial for its primary outcome or outcomes were described in Results and Conclusions sections of the Abstract, using a 10-category classification. Other outcomes were whether confidence intervals (CIs) and p values were presented for the main treatment comparisons, and whether the results and conclusions referred to measures of uncertainty. We estimated the proportion of papers that made claims that were not justified by the results, or were open to multiple interpretations.
Results 94 trial reports (120 treatment comparisons) were included. In Results sections, for 58/120 comparisons (48.3%) the results of the study were re-stated, without interpretation, and 38/120 (31.7%) stated that there was no statistically significant difference. In Conclusions, 65/120 treatment comparisons (54.2%) stated that there was no treatment benefit, 14/120 (11.7%) that there was no significant benefit and 16/120 (13.3%) that there was no significant difference. CIs and p values were both presented by 84% of studies (79/94), but only 3/94 studies referred to uncertainty when drawing conclusions.
Conclusions The majority of trials (54.2%) inappropriately interpreted a result that was not statistically significant as indicating no treatment benefit. Very few studies interpreted the result as indicating a lack of evidence against the null hypothesis of zero difference between the trial arms.
- clinical trials
- statistics & research methods
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Contributors SG designed the study, assisted with data extraction, performed the analysis and drafted the manuscript. EE collected the data, assisted with analysis and revised the manuscript.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors. SG is a National Institute of Health Research Senior Investigator.
Competing interests None declared.
Patient consent for publication Not required.
Provenance and peer review Not commissioned; externally peer reviewed.
Data availability statement Data are available in a public, open access repository (https://osf.io/chsva/files/).
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