%0 Journal Article
%@ 2369-2960
%I JMIR Publications
%V 11
%N 
%P e62828
%T Alternative Presentations of Overall and Statistical Uncertainty for Adults’ Understanding of the Results of a Randomized Trial of a Public Health Intervention: Parallel Web-Based Randomized Trials
%A Holst,Christine
%A Woloshin,Steven
%A Oxman,Andrew D
%A Rose,Christopher
%A Rosenbaum,Sarah
%A Munthe-Kaas,Heather Menzies
%+ Centre for Epidemic Interventions Research, Norwegian Institute of Public Health, Myrens Verksted 3L, Oslo, 0213, Norway, 47 48234044, Christine.Holst@fhi.no
%K communication
%K Grading of Recommendations Assessment, Development, and Evaluation language
%K GRADE language
%K statistical uncertainty
%K overall uncertainty
%K randomized trial
%D 2025
%7 18.3.2025
%9 Original Paper
%J JMIR Public Health Surveill
%G English
%X Background: Well-designed public health messages can help people make informed choices, while poorly designed messages or persuasive messages can confuse, lead to poorly informed decisions, and diminish trust in health authorities and research. Communicating uncertainties to the public about the results of health research is challenging, necessitating research on effective ways to disseminate this important aspect of randomized trials. Objective: This study aimed to evaluate people’s understanding of overall and statistical uncertainty when presented with alternative ways of expressing randomized trial results. Methods: Two parallel, web-based, individually randomized trials (3×2 factorial designs) were conducted in the United States and Norway. Participants were randomized to 1 of 6 versions of a text (summary) communicating results from a study examining the effects of wearing glasses to prevent COVID-19 infection. The summaries varied in how overall uncertainty (“Grading of Recommendations Assessment, Development and Evaluation [GRADE] language,” “plain language,” or “no explicit language”) and statistical uncertainty (whether a margin of error was shown or not) were presented. Participants completed a web-based questionnaire exploring 4 coprimary outcomes: 3 to measure understanding of overall uncertainty (benefits, harms, and sufficiency of evidence), and one to measure statistical uncertainty. Participants were adults who do not wear glasses recruited from web-based research panels in the United States and Norway. Results of the trials were analyzed separately and combined in a meta-analysis. Results: In the US and Norwegian trials, 730 and 497 individuals were randomized, respectively; data for 543 (74.4%) and 452 (90.9%) were analyzed. More participants had a correct understanding of uncertainty when presented with plain language (United States: 37/99, 37% and Norway: 40/76, 53%) than no explicit language (United States: 18/86, 21% and Norway: 34/80, 42%). Similar positive effect was seen for the GRADE language in the United States (26/79, 33%) but not in Norway (30/71, 42%). There were only small differences between groups for understanding the uncertainty of harms. Plain language improved correct understanding of evidence sufficiency (odds ratio 2.05, 95% CI 1.17-3.57), compared to no explicit language. The effect of GRADE language was inconclusive (odds ratio 1.34, 95% CI 0.79-2.28). The understanding of statistical uncertainty was improved when the participants were shown the margin of error compared to not being shown: Norway: 16/75, 21% to 24/71, 34% vs 1/71, 1% to 2/76, 3% and the United States: 21/101, 21% to 32/90, 36% vs 0/86, 0% to 3/79, 4%). Conclusions: Plain language, but not GRADE language, was better than no explicit language in helping people understand overall uncertainty of benefits and harms. Reporting margin of error improved understanding of statistical uncertainty around the effect of wearing glasses, but only for a minority of participants. Trial Registration: ClinicalTrials.gov NCT05642754; https://tinyurl.com/4mhjsm7s 
%R 10.2196/62828
%U https://publichealth.jmir.org/2025/1/e62828
%U https://doi.org/10.2196/62828