[Cosimo]

re: calculating standard deviation.

There used to be an Essays page here, but I can't find it. Mason's essay on calculating standard deviation was reprinted there. If you have Gambling Theory and Other Topics, I believe it's in there.

You will have different SDs at different levels, limit vs NL, full vs SH vs HU, different sites, and different games (HE vs Omaha vs Stud etc). Generally you can use 15 BB as your standard deviation.

If you calculate your EV and standard deviation, you will be able to calculate "for four hours at live play 10/20, I should win $56, with a standard deviation of $600." I believe those with huge databases that have charted the data are, indeed, getting Gaussian distributions of their session results. Poker winnings are discrete, of course, so the shorter the session and the fewer the sessions, the less proper such a graph will look.

SD is calculated as RMS of the differences between individual session results and the expected result from that session. "Expected result" here is just EV multiplied by time at the table. Yes, it is easy to calculate ...

... but confidence is very low. You have said that you've played 12 hours a day, two days a week, for three years. I'm guessing that is about 80,000 - 150,000 hands, depending on how precise and consistent you've been. That number of hands is about enough to have a confident assesment of your EV -- provided that your skills and the game didn't change during that time, both of which probably did change signifigantly.

So, again, precise values for standard deviation and EV are not really possible, and chasing them is not too useful.

You should find more on this topic by searching and/or posting in the Probability forum.