The effect of qualitative vs. quantitative presentation of probability estimates on patient decision-making: a randomized trial

Background Given the greater uncertainty surrounding probability estimates associated with qualitative (use of words or phrases) descriptions, the use of quantitative (numerical) information to communicate the risks and benefits of therapies is recommended but the impact of its use in decision aids is unexplored. Objective Using stroke prevention in atrial fibrillation as an example, to compare the impact of quantitative vs. qualitative descriptions of probability risk estimates in decision aids on the clinical decision‐making process. Design Randomized trial with a 2 × 2 factorial design. Subjects A total of 198 volunteers aged 60–80 years. Setting Outpatient clinics of a university‐affiliated, tertiary‐care teaching hospital. Methods Participants were asked to imagine that they had atrial fibrillation, and using a decision aid, were then randomized to two ways of receiving pertinent risk information regarding the probability of stroke and major bleeding when taking warfarin, aspirin or no therapy: (1) quantitatively, in which the 2‐year probabilities of stroke and major haemorrhage were presented both numerically and graphically with 100 faces (e.g. 8 of 100), and (2) qualitatively in which these probabilities were presented with the use of verbal phrases (e.g. very low, moderate). Outcome measures Primary: decisional conflict. Secondary: participants' choices, knowledge and expectations of outcomes using qualitative and quantitative scales. Results Participants reviewing quantitative risk information scored better on the informed subscale of the decisional conflict scale (P 0.05). Conclusions For participants