FC Groningen vs. Sparta Rotterdam: O/U 5.5

Research grade

⚖️ NeutralUnder at 75%

No measured edge, which here means a loss: the plain consensus (5+ holders, 60 %+, held to resolution) lost −3.0 % a trade after costs out of sample in the full-year test (n 86,296, 95 % CI −3.6 to −2.4 %).

• ≤ Spread or totalOct 22 backtest: spreads and totals −14.5 % a trade in spring (95 % CI −27 to −1), +1.5 % in October: no edge.
• · Favourite (60–95¢)Full year, out of sample: 0.70–0.90 lost −0.9 % a trade (n 26,050, 95 % CI −1.5 to −0.3): the least bad band, still a loss. The Oct 22 backtest's +0.4 % (n 4,327) was not confirmed.

The rules come from our Oct 22 2026 backtest (one entry per market, held to resolution, after a 1¢ half-spread and Polymarket's taker fees). Our full-year test without hindsight (Oct 26 2026) found none of them profitable out of sample, and the plain consensus lost −3.0 % a trade. The grade describes the market; it is not a forecast, not an edge and not advice.