Standard Deviation, $/per hour win rates, losing streaks

[Karatitis]

I'm posting this question to anyone who can show me how to calculate Standard Deviation for Texas Hold'em poker playing, given certain assumptions (which I will list in this post), and also to confirm what can one expect to win playing hold'em, and potential losing streaks as well.

I realize there are many variables other than just rake, and # of players taking the flop which determine success playing poker, but here goes: I am competent, fairly tight-aggressive player playing $10-$20, with a $5/half hour session fee, and have been winning by a very small $/hour approximately $7 per hour. My sample size is based on approx. 300 hours of play. Although, I have done much better playing short-handed, in particular 4-handed or fewer. The cardroom I frequent has a game that would be categorized as average-loose game, probably with about 5.5 - 6.0 players taking the flop (11-handed game), but I don't track statistics on average pot-size, etc.

Generally, what can one expect to realistically win from a $10-$20 game, assuming that ones has a positive expectation (i.e. the game is "soft")? Also, what is the calculation methodology for determining Standard Deviation for +- in any one session, or for a given sample-size? Lastly, what is the probability of having horrendous losing streaks of say, 8 or 9 consecutive losing sessions, with say an average loss during the streak of say $250? (Note: Session for me would be about an average of 7 hours).

I would appreciate anyone who can show me the calculations, or in the least, shed some light on how I can derive these figures. I'm in particular interest of the Standard Deviation for a session, and for a sample size of sessions.

Thanks,

Chris
Toronto, ON