Market Efficiency Score: Prediction markets offered 3% better odds than sportsbooks on Wednesday's Dream–Wings game

Ahead of Wednesday's WNBA meeting between the Atlanta Dream and the Dallas Wings, Dimers priced every venue offering the game on a single measure—the Market Efficiency Score, or how much margin each venue builds into its two-sided markets. The finding was consistent: prediction markets priced the game tighter than every traditional sportsbook. On the moneyline, prediction markets averaged a 101.87% overround against sportsbooks' 104.85%—a gap of nearly three points—and Polymarket posted the single tightest market of any venue at 101.0%.

What the Market Efficiency Score Measures

Every two-sided market—a moneyline, a spread, each side of a total—can be read as two implied probabilities. Add them together and an efficient market with no margin would sum to exactly 100%. In practice every venue sums to more than that, and the excess is the margin built into the price: the vig on a traditional sportsbook, or the effective pricing drag on a prediction market. The Market Efficiency Score is simply that sum. A market at 101% is tighter—better priced for the person trading it—than one at 105%.

One caveat up front: the Market Efficiency Score measures pricing, not accuracy. A tighter market is not necessarily a more correct read on who wins; it just means less margin sits between the two sides. This is a market-structure comparison, not a prediction and not a recommendation.

Atlanta Dream vs. Dallas Wings Moneyline: Efficiency by Venue

Ranked from tightest to widest, here is how every captured venue priced the Dream–Wings moneyline:

The three prediction markets—Polymarket, ProphetX and Novig—occupy the top three spots, each pricing the moneyline below any sportsbook on the board. The tightest sportsbook (theScore Bet, 104.71%) still sat more than a point and a half wider than the widest prediction market (Novig, 103.0%).

Dream vs. Wings Spread: Efficiency by Venue

The spread market told the same story. Prediction markets again led, with Polymarket tightest at 101.0%:

Total (Over/Under 179.5) is omitted from this edition: the full book-by-book total market was only partially available at capture. ProphetX displayed a 102.75% overround on its total, in line with its moneyline and spread pricing.

The Verdict: Prediction Markets vs. Sportsbooks for Dream vs. Wings

Averaged by venue type, prediction markets priced this game more efficiently than sportsbooks on both markets measured:

The mechanism behind the gap is structural. A traditional sportsbook sets its own lines and builds a house margin into both sides of every market; it is the counterparty to the person placing a bet, and the margin is how it makes money over time. A prediction market works differently—prices are set by traders buying and selling contracts against one another, and the platform takes a transaction fee rather than a built-in spread. On this game, that structural difference showed up as a measurably tighter price across the prediction-market venues. Whether that pattern holds across sports, favorites, and game states is exactly what the Market Efficiency Score is built to track over time.

The Three Prediction Markets Carrying Promo Code DIMERS for Dream vs. Wings:

All three prediction markets in this analysis are running a new-user offer under the same promo code—DIMERS—for this game:

The code DIMERS is the same across all three platforms. Full terms, eligibility, and step-by-step instructions are in each platform's dedicated guide: Polymarket promo code DIMERS, Kalshi promo code DIMERS, and ProphetX promo code DIMERS.

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Methodology & Disclaimer

The Market Efficiency Score is the overround of a two-sided market—the sum of both sides' implied probabilities. American odds were converted to implied probability (negative odds: −o ÷ (−o + 100); positive odds: 100 ÷ (o + 100)); prediction-market cent prices were used directly as implied probabilities. Prices were captured from Dimers' price tables and the ProphetX and Kalshi market screens at a single point in time ahead of the 8:00 PM ET tip-off. Lower overround indicates a tighter market; it does not indicate which venue is more likely to be correct on the outcome.

This is a market-structure analysis, not a prediction or a recommendation to trade or bet. Overround figures are computed from prices captured at a single point in time and change continuously. Prediction markets (Polymarket, Kalshi, ProphetX) are not sportsbooks; sportsbook and prediction-market pricing mechanisms differ. Must be 18+ (a higher minimum applies in some jurisdictions) and eligible under applicable law. Dimers.com may receive compensation through affiliate partnerships.