Purpose: All else equal, rare outcomes should be given relatively little weight in decision making. But, when strong emotions like disgust are present, objectively unlikely outcomes may feel more likely than they really are. We examined this possibility, which could account for preference-inconsistent decisions.
Method: In two pilot studies, we asked 3428 participants to rate 24 descriptions of health states on several dimensions to determine states that were rated the same on quality-of-life but differently on how disgusting they were. The pair that best fulfilled these criteria – chronic diarrhea and severe fatigue – was used in subsequent studies. In Study 1, we asked a different group of 3094 participants, "If you had to choose, would you prefer a [x]% chance of [condition], or a [x]% chance of death?" where x = 4% or 100% for both outcomes, and the condition was chronic diarrhea or severe fatigue. If people overweigh small probabilities of disgusting events like chronic diarrhea, we would expect them to choose death over diarrhea more often at 4% probability than at 100%. Substituting a less disgusting outcome, severe fatigue, should then lead to less inconsistency across probabilities. In Study 2, we presented another group of 300 participants with two hypothetical medical treatments, one with a 4% chance of death, and the other with a 4% chance of a complication, either chronic diarrhea or severe fatigue. Participants rated how likely each possible outcome felt, how vulnerable they felt to each outcome, and estimated their own particular chance of experiencing each outcome. We examined the relationship between these ratings and participants' trait disgust sensitivity.
Result: In Study 1 (see figure), people chose death over diarrhea significantly more often at 4% than at 100% (40% vs. 28%, chi-square=15.89, p<0.01), while preferences for fatigue versus death did not change across probabilities (30% vs. 34%, chi-square=1.92, p=0.18). This difference between conditions was more pronounced among lower-numeracy participants. In Study 2, trait disgust sensitivity significantly predicted both likelihood (r = 0.19, p < 0.01) and vulnerability (r = 0.12, p = 0.02) ratings across both conditions.
Conclusion: These results support the idea that disgust, a medically-relevant emotion, exaggerates people's tendency to overweight small probabilities. This occurs independent of quality-of-life concerns, and appears more prevalent among lower-numeracy individuals.