Cultivating credibility with probability words and numbers

• Main Authors: Robert N. Collins, David R. Mandel
• Format: Article
• Language: English
• Published: Society for Judgment and Decision Making 2019-11-01
• Series: Judgment and Decision Making
• Subjects: credibility; numeric probability; verbal probability; directionality; forecasts; accuracynakeywords
• Online Access: http://journal.sjdm.org/19/190912/jdm190912.pdf

Recent research suggests that communicating probabilities numerically rather than verbally benefits forecasters’ credibility. In two experiments, we tested the reproducibility of this communication-format effect. The effect was replicated under comparable conditions (low-probability, inaccurate forecasts), but it was reversed for low-probability accurate forecasts and eliminated for high-probability forecasts. Experiment 2 further showed that verbal probabilities convey implicit recommendations more clearly than probability information, whereas numeric probabilities do the opposite. Descriptively, the findings indicate that the effect of probability words versus numbers on credibility depends on how these formats convey directionality differently, how directionality implies recommendations even when none are explicitly given, and how such recommendations correspond with outcomes. Prescriptively, we propose that experts distinguish forecasts from advice, using numeric probabilities for the former and well-reasoned arguments for the latter.