V

Variance n.  The mathematical measurement of swings, i.e. how much something commonly varies from the average.  You may lose $20 per session on average, but usually range between +$110 and -$90.  The importance of variance in gambling cannot be overstated.  Larger bets cause greater swings, and even highly skilled individuals can be wiped out if they wager too much for their bankroll.  (Most players who think they are winners simply experienced positive variance, and conveniently forget the downturns.)  Many good players forego bets with only slight positive expectation because of high variance.  The statistical measure of variance is standard deviation.  The Kelly Criterion is a method of calculating bet size precisely in order to reduce risk of ruin.

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