answer to last night questions about statistical significance, found at Parkin's Lot:

50 in the universe, sample 33 or 44
100 in the universe, sample 49 or 80
200 in the universe, sample 65 or 132
500 in the universe, sample 81 or 217
1000 in the universe, sample 88 or 278
and so it goes till you find that an ideal sample for a 10% error margin hardly moves above 350 no matter how big the universe (it's 500 for 5%).