Multi-Outcome Markets and Why They Break Naive Analysis
A question with six possible answers is not six independent markets. What the outcome set implies, why the prices sum to about one, and what that enables.
Plenty of questions have more than two answers. Which candidate wins. Which month it happens. Which range the figure lands in. These are handled as sets of related contracts, and treating the members of a set as independent markets is one of the most common analytical errors.
The constraint
If the outcomes are mutually exclusive and collectively exhaustive, exactly one will be true. The prices must therefore sum to about one.
On an on-chain venue this is enforced by a real mechanism, not by convention: a complete set of outcome tokens can be minted from one unit of collateral and redeemed back for one unit. If the set trades for meaningfully less than one, buying and redeeming is profitable. If it trades for more, minting and selling is. How multi-outcome markets sum covers the general case.
Why the sum is never exactly one
Spreads. The sum of offers exceeds one; the sum of bids falls short. The gap between those two sums is the combined spread, and it is the cost of trying to exploit the constraint.
Missing outcomes. If the set has an "other" or "none of the above" and it is thin or absent, the remaining outcomes will not sum correctly and there is nothing wrong.
Staleness. One outcome that has not traded for a day drags the sum off. This is the most common cause and it is not an opportunity.
The long tail. Five candidates at one cent each contribute five cents and are individually overpriced. The favourite-longshot bias lives here.
What this enables
Consistency checks. Sum the best offers. If the total is below one by more than the combined cost of trading, look closer. Usually it is staleness. Occasionally it is real, and it is a cleaner signal than most cross-venue gaps because it involves one venue, one settlement rule and one moment in time.
Reading a distribution. A set of range contracts is a probability distribution. Read it as a shape rather than as a list of numbers and you learn far more: where the mass is, how fat the tails are, how confident the market is overall.
Better cross-venue matching. A binary elsewhere may correspond to several outcomes here combined. Matching them means summing the right subset, and getting the subset wrong produces a large and entirely fictitious gap. Matching markets across venues.
The traps
Non-exhaustive sets. If the listed outcomes do not cover every possibility, the sum should be below one. Treating that as an arbitrage is a mistake in reading the question.
Ambiguous "other". What happens if none of the named outcomes occurs is a resolution-criteria question, and these are exactly the criteria that get disputed. Disputes.
Correlated positions across a set. Holding several outcomes in one set is one position with a known payoff, not diversification. Correlated positions.
For comparison code
Any comparison system needs to know whether a market is a standalone binary or a member of a set, and if so which set. Getting this wrong produces confident nonsense, which is worse than producing nothing. This site refuses to pair markets it cannot match structurally, which is why the gaps table is shorter than people expect. How to read a gap table.
Next
Things that surprise people on an on-chain venue.
Educational content only. Nothing here is financial advice, a solicitation, or an offer to trade. Prediction markets can move against you and a position can lose its entire value. Where this guide describes a difference between venues it describes a theoretical cross-market edge in observed prices, which is not a profit: fees, spreads, capital lockup, transfer time and differing settlement rules all come out of it first.
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