ObjectivesTo assess the effectiveness of bar graph, pictograph and line graph compared with text-only, and to each other, for communicating prognosis to the public.DesignTwo online four-arm parallel-group randomised controlled trials. Statistical significance was set at p<0.016 to allow for three-primary comparisons.Participants and settingTwo Australian samples were recruited from members registered at Dynata online survey company. In trial A: 470 participants were randomised to one of the four arms, 417 were included in the analysis. In trial B: 499 were randomised and 433 were analysed.InterventionsIn each trial four visual presentations were tested: bar graph, pictograph, line graph and text-only. Trial A communicated prognostic information about an acute condition (acute otitis media) and trial B about a chronic condition (lateral epicondylitis). Both conditions are typically managed in primary care where ‘wait and see’ is a legitimate option.Main outcomeComprehension of information (scored 0–6).Secondary outcomesDecision intention, presentation satisfaction and preferences.ResultsIn both trials, the mean comprehension score was 3.7 for the text-only group. None of the visual presentations were superior to text-only. In trial A, the adjusted mean difference (MD) compared with text-only was: 0.19 (95% CI −0.16 to 0.55) for bar graph, 0.4 (0.04 to 0.76) for pictograph and 0.06 (−0.32 to 0.44) for line graph. In trial B, the adjusted MD was: 0.1 (−0.27 to 0.47) for bar graph), 0.38 (0.01 to 0.74) for pictograph and 0.1 (−0.27 to 0.48) for line graph. Pairwise comparisons between the three graphs showed all were clinically equivalent (95% CIs between −1.0 and 1.0). In both trials, bar graph was the most preferred presentation (chosen by 32.9% of trial A participants and 35.6% in trial B).ConclusionsAny of the four visual presentations tested may be suitable to use when discussing quantitative prognostic information.Trial registration numberAustralian New Zealand Clinical Trials Registry (ACTRN12621001305819).