[westiseast]

If I've understood it correctly, the smaller your sample size, the bigger the difference you need between response rates. So if the difference is 60%, then a sample of 30 people can be statistically significant. But if you're looking for a 5% improvement on something, you'll need to sample a large number of people.

I just used this:

http://www.prconline.com/education/tools/statsignificance/in...