Measles cases in U.S. in 2026?

CalibrationLe (2026) shows all domains compress toward 50% at long horizons, meaning long-dated markets systematically underprice certainty in both directions — if the true probability is well below 50%, the market price is probably still being pulled artificially toward 50% by the horizon effect, offering edge to No traders willing to hold. Polymarket's 67% outcome-correctness rate (Clinton & Huang 2025) is the lowest of major platforms, suggesting Polymarket crowds are more often wrong than Kalshi or PredictIt — this market's price should be treated with more skepticism than its apparent consensus implies.

RisksThis market has a long horizon with daily volatility above 5%, meaning position sizing matters enormously — a trader who takes a full position early and is correct directionally can still lose money if volatility forces them out before the case count becomes clear. Measles outbreaks are geographically and socially clustered (unvaccinated communities), so the case count has fat-tail upside that's hard to model from early-year data, creating asymmetric risk for holders of the No side if a major outbreak ignites in a dense population center.