Objectives: To assess the impact on readers’ interpretation of the results reported in an abstract for a hypothetical clinical trial with 1) a statistically significant result, 2) spin, 3) both a statistically significant result and spin compared to 4) no spin and no statistically significant result.

Participants: Health students and professionals from universities and health institutions in France and the UK.

Interventions: Participants completed an online questionnaire using Likert scales and free text, after reading one of the four versions of an abstract about a hypothetical randomized trial evaluating “Naranex” and “Bulofil” (two hypothetical drugs) for chronic low back pain. The abstracts differed in a) reported result of “mean difference of 1.31 points (95%CI 0.08 to 2.54; p= 0.04)“ or “mean difference of 1.31 points (95%CI -0.08 to 2.70; p= 0.06)” and b) presence or absence of spin. The effect size for the trial’s primary outcome (pain disability score) was the same in each abstract; slightly in favour of Naranex.

Primary outcome: The reader’s interpretation of the trial’s results, based on their answer (1: disagree, 4: neutral, 7: agree) to the following statement: “About the main findings of the study, what is your opinion about the following statement: ‘Naranex is better than Bulofil’?”

Results: 297 of the 404 people randomized to receive one of the four abstracts completed the study. Respondents were more likely to favour Narenex when the abstract reported a statistically significant result without spin; a statistically significant result with spin, a non-statistically significant result with spin, compared to when it reported a non-statistically significant result without spin.

Conclusions: Statistical significance appears to have influenced readers’ perception whatever the level of spin, while spin influenced readers’ perception when the results were not statistically significant but did not appear to have an impact when results were statistically significant

People informed and consenting in participating in the study could submit their email address through an online form. Participants completed an online questionnaire hosted in framaforms.org using Likert scales and free text, after reading one of the four versions of the experimental abstract.