posted and then totally forgot about this thread. Since I'm a dork, i keep track of this sort of thing in an excel worksheet along with daily play. Calculations are pretty similar to those found in
Homer's now famous thread
the upper bound of your confidence interval can be found with the equation:
=J-NORMSINV((100-L)/200)*K*(1/SQRT(I/100))
where J is BB/100, L is your confidence interval (is use 95 for 95%), K is your standard deviation/100, and I is your number of hands.
the lower bound can be found with the same equation, except it starts with J- instead of J+
so if i've seen 5BB/100 over 20,000 hands with a SD of 40BB/100, i can say with 95% confidence my true win rate is between 10.54BB/100 and -0.54BB/100.
What i've learned from doing these calculations is, they don't tell us that much. The OPs case isn't much different. He obviously isn't killing the game, but there's about a 1/3 chance that he isn't playing losing poker over that stretch either.