[Zetack]

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Variance is a measure of the dispersion of profit, usually measured per hour or per 100 hands. People actually talk about standard deviation, which is the square root of variance, more than variance itself.

One way to think about it is about 2 times out of 3, your results will be within one standard deviation of your long-term expectation. So if you are a +2 BB/hour player with a standard deviation of 20 BB/hour, about 1 time in 6 you'll lose more than 18 BB in an hour, 1 time in 3 you'll be between -18 BB and +2 BB, 1 time in 3 you'll be between +2 BB and +22 BB, and 1 time in 6 you'll win more than 22 BB in an hour.

Low variance is good because you can play at higher stakes for the same bankroll, and you can know your expected win rate more precisely.

There's no one-size-fits-all answer to which kind of poker has the highest or lowest variance. It doesn't depend only on the table and limit structure, it depends on the playing styles of the people. In no limit, it also depends on the size of stacks relative to the blinds.

Your first thought would be no limit variance is higher, due to the occassional very large pot. But the potential for large pots means people take fewer chances. In the no limit games I play variance is generally higher than limit games, but I wouldn't extrapolate that to all games.

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A much simpler way to explain variance is to simply say its about swings. A game with a lot of variance has big swings up and down.

So if you have say a winrate of 1.8 BB/100 and you play 500,000 hands over the next year, you can say with pretty good confidence that you'll be pretty close to a certain number of BB's up at the end of the year. But because of variance you may be hugely down or hugely up over some small subsection of hands during that stretch.

People tend not to be wild about varience because nobody likes the downswing side of varience.

Having said that, I have no idea what form of poker is innately swingier.

--Zetack