Predicting in shock: on the impact of negative, extreme, rare, and short lived events on judgmental forecasts

The occurrence of unexpected events that are extreme in magnitude, rare in frequency, and short-lived in duration poses distinctive challenges to decision makers and planners. In this paper we examine the impact of negative versions of these events, which we term “shocks”, on the judgmental forecasts of subjects experiencing them. A behavioral experiment asking participants to forecast monthly time series in the presence of temporary but extreme decreases in those series is used. Average changes to annual prediction intervals and 1-month ahead forecasts were much smaller than the magnitude of the shock and occurred in proportion to the size of the shock. Changes to prediction intervals were more persistent for moderate than large shocks, and larger for shocks occurring a second time. Our results provide supporting evidence for the view that decision makers underweight rare and extreme events rather than overweight them, consistent with a discounting or forgetting effect. The behavioral findings are relevant to operations researchers involved in expert judgment elicitation and in supporting decision making.