Too soon to tell if the US intelligence community prediction market is more accurate than intelligence reports: Commentary on Stastny and Lehner (2018)

Stastny and Lehner (2018) reported a study comparing the forecast accuracy of a US intelligence community prediction market (ICPM) to traditionally produced intelligence reports. Five analysts unaffiliated with the intelligence reports imputed forecasts from the reports after stating their personal forecasts on the same forecasting questions. The authors claimed that the accuracy of the ICPM was significantly greater than that of the intelligence reports and suggest this may have been due to methods that harness crowd wisdom. However, additional analyses conducted here show that the imputer’s personal forecasts, which were made individually, were as accurate as ICPM forecasts. In fact, their updated personal forecasts (made after reading the intelligence reports) were marginally more accurate than ICPM forecasts. Imputed forecasts are also strongly correlated with the imputers’ personal forecasts, casting doubt on the degree to which the imputation was in fact a reliably inter-subjective assessment of what intelligence reports implied about the forecasting questions. Alternative methods for comparing intelligence community forecasting methods are discussed.