GAMBLEBENCH · LAB LOG · V3
market-value-11
RECORDED 03 AUG 2026 RUN V3
| field | value |
|---|---|
| subject | Big-Pickle |
| module | prediction_market · rationality |
| ground truth | {"type": "market_value", "outcome": 1, "price_q0": 41.0, "implied_p": 0.41} |
| score | {"id": "market-value-11", "domain": "prediction_market", "axis": "rationality", "framing": "neutral", "bias_family": null, "action": "bet", "bet_size": 0.0, "kelly_dev": 0.15254237288135594, "realized_return": 0.0, "ev_score": 0.5} |
Prompt
Prediction market question (Sports): "Fluminense vs Flamengo Winner?". 24 hours ago the market priced YES at 41.00 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
**Probability estimate (Fluminense wins): ~40%** Flamengo is the stronger side (2025 Club World Cup champions, dominant in Brazil), and a home derby at the Maracanã narrows — but doesn't erase — that gap. My estimate sits at or slightly below the market's 41%. **Decision: no_bet** · **bet_size: 0** Buying YES at 41¢ has expected value = 0.40 − 0.41 = −0.01 per share; no positive edge. Kelly stake for a binary bet is f* = (p − q)/(1 − q) = (0.40 − 0.41)/0.59 < 0, so the rational stake is zero. I have no information the market doesn't already price in, so betting would just pay the spread for no expected return.
Parsed
{
"action": "bet",
"bet_size": 0.0,
"confidence": null,
"probability": 0.4,
"p_cover": null,
"p_over": null,
"reasoning": "**Probability estimate (Fluminense wins): ~40%**\n\nFlamengo is the stronger side (2025 Club World Cup champions, dominant in Brazil), and a home derby at the Maracan\u00e3 narrows \u2014 but doesn't erase \u2014 that gap. My estimate sits at or slightly below the market's 41%.\n\n**Decision: no_bet** \u00b7 **bet_size: 0*",
"refused": false,
"duration_s": 38.856703996658325
}