Maximize Gains, Minimize Ruin: The Kelly Criterion's Dual Nature

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The Kelly Criterion provides a strategic framework for determining the optimal percentage of a bankroll to wager, which aims to maximize expected returns while minimizing the risk of total loss. It quantifies the appropriate bet size based on the probability of winning compared to losing, encouraging a conservative betting strategy to avoid ruin. Critics argue that the Criterion is overly cautious, especially in contexts where bettors are willing to risk bankruptcy. In scenarios like the St. Petersburg Paradox, where one can repeatedly engage in high-risk, positive expected value bets with a slight edge, the contradiction arises: though the expected value is infinite with consistent betting, the practical likelihood of enduring all risks—as the number of bets increases—approaches zero. This highlights a dichotomy in gambling strategies: balancing maximum profit potential against the realistic risk of total financial loss.

Being rational necessarily involves engagement with probability. Given two possible courses of action, it can be rational to prefer the one that could possibly result in a worse outcome, if there's also a substantial probability for an even better outcome. But one's attitude toward risk -- averse, tolerant, or even seeking -- also matters. Do we work to avoid the worse possible outcome, even if there is potential for enormous reward? Nate Silver has long thought about probability and prediction, from sports to politics to professional poker. In his his new book On The Edge: The Art of Risking Everything, Silver examines a set of traits characterizing people who welcome risks.

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Blog post with transcript: https://www.preposterousuniverse.com/podcast/2024/08/12/285-nate-silver-on-prediction-risk-and-rationality/

Nate Silver received a B.A. in economics from the University of Chicago. He worked as a baseball analyst, developing the PECOTA statistical system (Player Empirical Comparison and Optimization Test Algorithm). He later founded the FiveThirtyEight political polling analysis site. His first book, The Signal and the Noise, was awarded the Phi Beta Kappa Society Book Award in Science. He is the co-host (with Maria Konnikova) of the Risky Business podcast.

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