There is a very remote chance of inciting fear: The effects of magnitude and modal probability phrases on decision-making

Health organizations tend to use verbal probability phrases such as “very rarely” or “there is a chance” to convey risk information to the public. Phrases like “very rarely” attempt to describe the small magnitude of the risk while phrases like “there is a chance” merely indicate that the event is possible, without focusing on how improbable it is. Both are used to describe probabilities of similar magnitudes, even though the phrases might be interpreted very differently by the public. This could be problematic because public health organizations presumably do not intend to inflate risk perceptions with such wording differences. In this study, I asked participants, randomly assigned to one of three experimentally manipulated contexts, to make a hypothetical decision. Within these contexts, participants received risk information in one of seven formats. Two of these formats used a “magnitude” probability phrase, describing the small probability of an adverse event. Another two formats used a “modal” probability phrase, which merely highlights the possibility of the event. In three other groups, participants received the risk information in the form of a numerical probability. I found that receiving risk information in a modal format resulted in decisions reflecting a larger perceived probability that the adverse event will occur compared to when the magnitude phrases were used. I also examined how each phrase affects decision-making with special emphasis placed on comparing pairs of verbal and numerical phrases. These results contribute to a better understanding of how people interpret probabilistic information used in a variety of contexts while also employing a novel methodology that could potentially be used in the future for further research.