A large sample size gives you confidence that your estimates are correct.
If they're too small to be interesting, you can say that they are too small to be interesting.
500 is not a large sample size. The paper by Bland that I cited earlier reviewed two medical journals and found the median sample size was about 3000.
Another way to think about a sample size of 500 is to look at the confidence intervals of the correlation, before you've controlled for anything, a correlation of r = 0.3 has CIs of 0.22 to 0.38 - that's a huge confidence interval. And square it to get
proportion of variance, our CIs go from (about) 0.04 to 0.15 - 4 times larger(!!). "Yeah, maybe we've accounted for 4% of the variance, or maybe 15%." That's not very certain.
Jeremy
Security System.