Arbitrage Between Prediction Markets: Why One Question Trades at Two Prices

Open the same question on two prediction venues, and the quotes often disagree. One platform might show Yes at 58 cents while another asks 63 cents for what looks like an identical outcome. Textbook economics says arbitrage should erase that difference within minutes. Real prediction market prices can stay apart for days or weeks, and the reasons say a lot about how these venues work. Below: what two prices for one question mean, seven forces that keep them apart, the arithmetic once costs enter, and how venue rules treat prediction market arbitrage.