Why Prediction Market Odds Are Not Literal Probabilities

Empirical studies of hundreds of thousands of settled contracts confirm that market-implied probabilities generally track realized outcomes with high precision. In liquid markets, these tools frequently outperform individual experts and polls because the financial incentive structure rewards accuracy while punishing error. However, this accuracy is not a constant; it is a market-clearing number influenced by five distinct distortions that seasoned participants must account for.

The most pervasive issue is the favorite-longshot bias, where low-priced contracts win less often than their odds imply, while expensive ones offer slightly better returns. Compounding this is the capital lock-up effect: because collateral remains frozen until settlement, long-dated contracts trade at a discount to reflect the opportunity cost of that idle money. Furthermore, market quality is rarely uniform. While political and macroeconomic markets often feature tight spreads and professional participation, thin markets on obscure topics often lack the volume to generate reliable signals.

Transaction costs and resolution risk round out the list of variables that separate a price from a true probability. Fees and spreads can erode a trader's edge, while the specific legal or oracle-based resolution criteria can occasionally lead to unexpected outcomes regardless of the actual event. For the analyst, the takeaway is clear: view prediction market prices as a strong, evidence-based prior, but never as an unvarnished fact. A responsible reading requires adjusting for the horizon, checking liquidity, and applying a mental haircut for the structural risks inherent in how these contracts settle.