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Variance

Variance is how far real results stray from what the odds and the chances predict. In betting it is large: good bets can lose for weeks before the edge shows.

Example

100 bets of 10 at 2.75 on a 40% chance expect a profit of 100, but one standard deviation is about 135 either side.

Go further

What variance does to a good betThe full explainer, on the blogExpected value calculatorWhat a bet makes on average, its edge, and the swing over many bets.

Related terms

Expected value (EV)Expected value is what a bet makes on average if placed many times: stake × (probability × decimal odds − 1). A positive EV means the odds beat the chance.Betting unitA betting unit is a fixed standard stake, usually 1% to 2% of the money set aside for betting. Bets are sized in units, so results compare across bankrolls.Regression to the meanRegression to the mean is the tendency of an extreme run to be followed by results closer to average, because part of any extreme run is luck.