An index for betting with examples from games and sports.

It is tempting to accept bets when the outcome has a positive expectation favouring the bettor. We examine situations where this is not enough of a criterion as a basis for betting. The argument we present shows that the probability of winning the bets in the long run has to be qualified in a certain way beyond positive expectation. We introduce an alternative index as a criterion to recommend to bettors. [ABSTRACT FROM AUTHOR]