Fig. 1

Experimental paradigm and measurements scales. A Study design. Exercises focusing on vaccine efficacy and p value were presented in a random order, while the exercise about test results interpretation was always the last. In this figure section, the letters B and C, respectively, refer to sections B and C from Fig. 1, each section describing the response interface used for some questions. The full survey content including sentences of context, questions as well as explanations is provided in Annex of Additional file 1. B A double-sided visual analog scale was used in exercises about vaccine efficacy and p value as well as in the five theoretical questions of the exercise about test results interpretation to collect simultaneously participants’ accuracy (side of the cursor) and confidence (distance to the center/extremity of the scale) on each claim. Instructions given to the participants To give your answer, move the slider on the scale: the more hesitant you are about your answer, the closer the slider should be placed to the middle, the more confident you are about your answer, the closer the slider should be placed to the extremity of the scale. If you don't know and you answer randomly, place the slider on the center. C The practical PPV calculation task of the exercise focused on test results interpretation used two paired visual analog scales: participants indicated their PPV estimation (ranging from 0 to 100%) by moving the first cursor on the first visual analog scale, and then reported their judgment of confidence by adjusting the width of a blue zone of uncertainty around the first value using the second cursor of the second visual analog scale (width of blue zone = 0.02 * confidence²). The lower the judgment of confidence, the more extended the blue area. Instructions given to the participants To answer, move the first slider on the scale to indicate your answer, then adjust your confidence level by moving the second slider