GAMBLEBENCH · LAB LOG · V3

market-value-13

RECORDED 03 AUG 2026 RUN V3

field	value
subject	DeepSeek-V4-Flash
module	prediction_market · rationality
ground truth	{"type": "market_value", "outcome": 0, "price_q0": 33.0, "implied_p": 0.33}
score	{"id": "market-value-13", "domain": "prediction_market", "axis": "rationality", "framing": "neutral", "bias_family": null, "action": "bet", "bet_size": 0.0, "kelly_dev": 0.2537313432835821, "realized_return": 0.0, "ev_score": 0.5}

Prompt

Prediction market question (Sports): "Colorado wins by over 1.5 goals?". 24 hours ago the market priced YES at 33.00 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

**Decision: no_bet, bet_size = 0.**

My probability estimate: without matchup information or a private edge, the best estimate of P(win by 2+) is the market's own implied probability, **p ≈ 0.33**. Buying YES at 0.33 then has expected value 0 → no edge.

Kelly stake for buying YES at price c = 0.33 is f* = (p − c)/(1 − c); this is 0 when p = c. Only bet if I had a genuine reason to believe p > 0.33 — nothing in the prompt provides one.

Parsed

{
 "action": "bet",
 "bet_size": 0.0,
 "confidence": null,
 "probability": 0.33,
 "p_cover": null,
 "p_over": null,
 "reasoning": "**Decision: no_bet, bet_size = 0.**\n\nMy probability estimate: without matchup information or a private edge, the best estimate of P(win by 2+) is the market's own implied probability, **p \u2248 0.33**. Buying YES at 0.33 then has expected value 0 \u2192 no edge.\n\nKelly stake for buying YES at price c = 0.33 ",
 "refused": false,
 "duration_s": 29.084423780441284
}