Variance
What does "variance" mean in sports betting?
How far actual results swing around what you would expect on average. Higher variance means bigger short-run swings, up and down.
Even a bet with an edge loses often, and losses can bunch together. Variance is why a good process can show a losing week and a bad one can show a winning week.
The longer your sample, the more results settle toward your true expected value. Flat unit sizes and a bankroll big enough to ride out swings help you survive the short run.
Example
You make 100 bets of $110 at -110, each with a true 55% chance to win. Expected profit is +$550, but the standard deviation is about $1,045. You would still be down money after those 100 bets about 31% of the time.
Related terms
Expected value (EV)
Expected value (EV) is the average amount a bet would win or lose per play if you could make it many times. Positive EV (+EV) means the price is better than the true chance.
Unit
A unit is a fixed slice of your bankroll, commonly 1% to 2%, used to size every bet so stakes stay consistent.
Regression to the mean
The tendency for an extreme result to be followed by one closer to average, because luck helped make the first one extreme.
Drawdown
The drop from your bankroll's highest point to its lowest point before it sets a new high. It measures how deep a losing stretch went.
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