What is variance?

You may have noticed a word cropping up in poker players’ vocabulary a bit more often lately. People have always talked about luck and bad beats in poker, but now you’re more likely to hear the term ‘variance’ to describe the ups and downs of our beloved game.

Most solid players have an idea of just how good they are..You’d know, for example, how much money you made or lost per hand at a certain level, or per tournament buy-in. That amount would be a kind of batting average – or the ‘norm’ for your level of play. This is also sometimes called your expectation – the amount you can expect to make or lose on average.

The problem with expectation in the short-term though comes when players hit either a good or bad spell of luck that can skew results one way or another.  Taking this into account we can then use the highly talked about variance model as a measure of the amount your results deviate from your expectation.  

Are you a luck-box?

For instance most people know that Aces versus Kings all-in pre-flop is about 80/20 in favour of the Aces. That means that if you ran enough trials, the Aces would win 80% of the showdowns on average. Now, imagine you only dealt that same match-up ten times. Obviously, on average the Aces would win eight times and the Kings would win two, but assuming you did hundreds of trials of ten showdowns, how often would it end up being 7-3 to the Aces? How many times would it actually end up 8-2 to the Kings?! In everyday terms, this is what measuring variance attempts to understand.

In order to measure variance properly you need to record your results for a great length of time and probably use a statistics package to get the final figure. Fortunately, you don’t need to get down to the nitty maths to understand the various principles which govern variance. In fact, it’s these very principles that are covered in the next article in this series, ‘Variance and game selection’.

Read Part 2...