In fact, there do exist probability distributions without any (finite) average. Suppose, for example, that there were a 1/2 chance of the job staying up for one day, a 1/4 chance of it staying up for two, a 1/8 chance of it staying up for four, and in general a 1/2n+1 chance of it staying up for 2n days for all integer n ≥ 0. If you try to work out the expected average length of time for one to stay there, you'll find you end up with infinity – and yet it's a perfectly meaningful probability distribution.
Not that I'm suggesting that AQA's job adverts do in fact follow this pattern or anything like it, but it is at least possible in theory :-)
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Date: 2007-02-21 03:43 pm (UTC)Not that I'm suggesting that AQA's job adverts do in fact follow this pattern or anything like it, but it is at least possible in theory :-)