Navigating doubt: The impact of scientific uncertainty in health communication and the role of recipient literacy and uncertainty intolerance

Background: Uncertainty is an important and frequently studied topic in health communication. It can be caused by many different sources. However, research in which the effects of different sources of uncertainty are compared is limited, and little is known about the impact of recipient characteristics on these effects.
Aims: We investigate whether different sources of message uncertainty impact perceived medication effectiveness and behavioral intentions. In addition, we explore the potential impact on message credibility, as well as the moderating role of recipients’ intolerance of uncertainty, science literacy, and health literacy.
Methods: In our preregistered, online between-subjects experiment, we manipulated the independent variable ‘uncertainty of the medicine’s effectiveness’. Participants (N = 946, Dutch) were asked to imagine that they suffered from a severe headache for which existing medication proved ineffective. Subsequently, they were randomly exposed to one of four experimental messages. In the certain outcome condition, the message communicated that a recently introduced medicine will be effective in reducing this type of headache. In the three uncertain outcome conditions, the message read that effectiveness was unsure for different reasons; i.e., limited scientific evidence, expert disagreement, or conditional effectiveness.
Results: The certain outcome message resulted in higher perceived effectiveness of the medicine and higher intentions to take the medicine compared to the conditions presenting an uncertain outcome. There were no differences in perceived effectiveness and intentions to take the medicine between the three uncertain conditions. Furthermore, the uncertainty sources did not impact perceived message credibility, nor did uncertainty intolerance, science literacy, or health literacy play a moderating role.
Discussion: Our study concludes that communicating uncertainty about a new treatment decreases the perceived effectiveness and acceptance of this treatment, but this effect does not depend on the source of the uncertainty.