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I've had a horrible past few days...overpairs running into sets, lower 2prs running into higher 2prs, lower flushes running into higher ones...all this combined w/ just general cold cards and missed flops. Is this what variance refers to?
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Luck is the cause of variance, but this isn't quite what it refers to.
Variance and win rate are the two measures of a player's style. Both can beasured in BBs per hour, and both numbers are needed to determine the player's necessary minimum bankroll.
If someone is incredibly loose and aggressive preflop, but plays well postflop, he might have a Win rate of 5 BBs per hour, with a variance of 300 BBs per hour. This means that 99% of the individual hours that he plays will be within the range -295 to +305 in BBs lost/won. (This is actually not true, because no one plays exactly the same hour over hour. But the analysis becomes true as you average out the different hours.
It seems like you could never count on winning money with these numbers, but the important thing is that the win rate is always multiplied times the number of hours, where the variance is multiplied by the square root of the number of hours. Therefore, with the stats above:
<font class="small">Code:</font><hr /><pre>
Hours exp. win exp. variance result range
1 5 300 -295 to +305
4 20 600 -580 to +620
100 500 3000 -2500 to +3500
900 4500 9000 -4500 to +13500
3600 18000 18000 0 to +36000
10000 50000 30000 +20000 to +80000
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Hmmm. I see in my preview that this bulletin board doesn't support the code tags correctly. Paste the table into Word and set the font to courier
You can see why so many people are derisive when someone comes on and says, "I've been crushing this game for TWO WHOLE WEEKS!" It takes a lot of hours to reach the long term. If you instead assume that the player is terrible, and has an expected win of negative 5 BBs, you can see that he could still be at +4500 BBs at the end of 900 hours of play, if he were very lucky. Eventually, though, the luck will be swamped, but it takes thousands of hours, not hundreds.
Note that the result range is what he is 99% likely to fall in. There is always the 1% possibility of falling outside this range, but that's why we call it gamblin'.