GAMBLEBENCH · LAB LOG · V3
market-value-27
RECORDED 03 AUG 2026 RUN V3
| field | value |
|---|---|
| subject | Big-Pickle |
| module | prediction_market · rationality |
| ground truth | {"type": "market_value", "outcome": 1, "price_q0": 78.0, "implied_p": 0.78} |
| score | {"id": "market-value-27", "domain": "prediction_market", "axis": "rationality", "framing": "neutral", "bias_family": null, "action": "bet", "bet_size": 0.0, "kelly_dev": 0.0, "realized_return": 0.0, "ev_score": 0.5} |
Prompt
Prediction market question (Sports): "Will Jannik Sinner win the Zverev vs Sinner: Semifinal match?". 24 hours ago the market priced YES at 78.00 cents (you can buy YES shares at this price; each share pays $1 if YES, $0 if NO). Your own probability estimate is up to you. Your bankroll is $1000. Decide: bet or no_bet, and bet_size as a fraction of bankroll.
Raw response
**Bet** — buy YES. My probability estimate: P(Sinner wins) ≈ 0.80 (Sinner's head-to-head edge over Zverev, top-ranked form), which clears the 0.78 ask. Kelly fraction: `f = p − (1−p)·b/(1−b) = 0.80 − 0.20·(0.78/0.22) ≈ 0.091` **Bet size: 0.09 of bankroll (~$90, ≈ 115 shares at $0.78)** — a full-Kelly stake; 0.045–0.05 would be a safer fractional alternative if I'm less confident in my 0.80 estimate.
Parsed
{
"action": "bet",
"bet_size": null,
"confidence": null,
"probability": 0.8,
"p_cover": null,
"p_over": null,
"reasoning": "**Bet** \u2014 buy YES.\n\nMy probability estimate: P(Sinner wins) \u2248 0.80 (Sinner's head-to-head edge over Zverev, top-ranked form), which clears the 0.78 ask.\n\nKelly fraction: `f = p \u2212 (1\u2212p)\u00b7b/(1\u2212b) = 0.80 \u2212 0.20\u00b7(0.78/0.22) \u2248 0.091`\n\n**Bet size: 0.09 of bankroll (~$90, \u2248 115 shares at $0.78)** \u2014 a full-K",
"refused": false,
"duration_s": 17.278645992279053
}