Two Measures of Incoherence: How Not to Gamble If You Must

Mark J. Schervish, Teddy Seidenfeld and Joseph B. Kadane


The degree of incoherence, when previsions are not made in accordance with a probability measure, is measured by either of two rates at which an incoherent bookie can be made a sure loser. Each bet is considered as an investment from the points of view of both the bookie and a gambler who takes the bet. From each viewpoint, we define an amount invested (or escrowed) for each bet, and the sure loss for incoherent previsions is divided by the escrow to determine the rate of incoherence. Potential applications include the treatment of arbitrage opportunities in financial markets and the degree of incoherence of classical statistical procedures. We illustrate the latter with the example of hypothesis testing at a fixed size.

Keywords: Bookie, Coherence, Escrow, Gambler, Rate of arbitrage.

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