Whether Is Not When: Separating Occurrence from Timing in Polymarket Prices
Sizheng Fan, Yinghe Sun, Rong Zhao
原文摘要
Prices formed by Web users on Polymarket, a blockchain-based prediction market, are now cited in the news and in a U.S. Army intelligence bulletin as early warnings of geopolitical events. However, it remains unclear whether these prices can serve as such warnings. This cannot be judged from accuracy, because most markets resolve No and accuracy can remain high even when many of the events that did happen are missed. In this paper, we study this question from two aspects, using all 1.24 billion on-chain trades in 2.37 million Polymarket markets through September 2026. First, from 3,686 markets on geopolitical conflicts, we derive 208 unscheduled events that did happen and measure how far in advance prices move before the first Web report of each event. Second, we separate the information in prices about whether an event happens from the information about when it happens. To do so, we group 1,551 contracts into 338 deadline ladders and read each ladder as one forecast of the event date. We then split its log score, and the profit of 9.3 million trades by 491,000 accounts, exactly into these two parts. We find that one day before they were reported, prices correctly predicted only 56% of the geopolitical events but all 51 scheduled central-bank decisions. Separating the two parts shows that only about one eighth of the information in prices concerns timing. A small group of large accounts earns timing profits, but beyond current prices, no group of accounts helps predict an event within days. A high price is therefore a sign that an event is likely rather than imminent. Near-term warnings read from the whole ladder are more often right than those read from a single contract. Platforms should report recall alongside accuracy, and show near-term probabilities read from the whole ladder.
cs.CY