Scholars, practitioners, and pundits often leave their assessments of uncertainty vague when debating foreign policy, arguing that clearer probability estimates would provide arbitrary detail instead of useful insight. We provide the first systematic test of this claim using a data set containing 888,328 geopolitical forecasts. We find that coarsening numeric probability assessments in a manner consistent with common qualitative expressions—including expressions currently recommended for use by intelligence analysts—consistently sacrifices predictive accuracy. This finding does not depend on extreme probability estimates, short time horizons, particular scoring rules, or individual attributes that are difficult to cultivate. At a practical level, our analysis indicates that it would be possible to make foreign policy discourse more informative by supplementing natural language-based descriptions of uncertainty with quantitative probability estimates. More broadly, our findings advance long-standing debates over the nature and limits of subjective judgment when assessing social phenomena, showing how explicit probability assessments are empirically justifiable even in domains as complex as world politics.
Friedman, Jeffrey A., Joshua D. Baker, Barbara A. Mellers, Philip E. Tetlock, and Richard Zeckhauser. "The Value of Precision in Probability Assessment: Evidence from a Large-Scale Geopolitical Forecasting Tournament." International Studies Quarterly 62 (June 2018): 410-422.