What is prediction market probability? Theory + practice
The probability you see on Polymarket isn't a true probability — it's a crowd bet. Here's how prediction markets are SUPPOSED to work and where they diverge.
Prediction markets are built on a simple theoretical claim: if enough people bet real money on an event, the price will converge to the true probability. This is the Efficient Market Hypothesis applied to prediction markets — and like its stock-market cousin, it's half true.
The theoretical case
Suppose a market trades at 60¢ YES on “Team A wins,” but the true probability is 70%. A rational bettor buys YES at 60¢, expecting 70¢ payout per contract on average. More rational bettors join, pushing the price up to 70¢. Once price = true probability, edge disappears, trading volume falls. “Converged.”
This is elegant, and it's why Polymarket prices are often informative. But several assumptions have to hold:
- Enough rational bettors with capital
- Enough time for convergence
- Markets are liquid enough that bets move price
- Information spreads freely
Reality: all four assumptions break
- Not enough capital: many markets have under-$10k liquidity. A rational whale could move price, but they need better returns elsewhere.
- Not enough time: fast-moving events (elections, sports) resolve before equilibrium reaches.
- Crowd bias: Polymarket skews crypto-native, right-leaning, US-centric. Biases show up systematically.
- Information asymmetry:some bettors have timely info (sports lineups, political insider baseline); others don't.
The edge = gap between price and probability
Your job isn't to predict events — it's to find markets where the crowd is systematically mispricing. Tools like PolyGuru's mispricing detector do exactly this: compare the crowd price against a calibrated probability informed by real-world research, sharp-book consensus, and historical base rates.
Sanity check: when is 65¢ really 65%?
On deep-liquidity markets (> $1M), with days of trading time, and well-known public information, price usually ≈ probability. Here, edge is small and hard to find.
On thin, fast-moving, information-asymmetric markets, price can diverge 10-20pp from probability for extended periods. These are where PolyGuru's picks cluster.
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