Reporting and interpretation of results from clinical trials that did not claim a treatment difference: survey of four general medical journals

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.