Hi, noob here, couldn't find this anywhere by searching.
i use 3000-5000 impressions
20k+ impressions for me, ive had images sit at 7k impressions and had like 0.09ctr and then at 20k+ impressions, it was @ ~.25+
did you find that was related to time of day?
I don't look at impressions really, I try to make my campaigns profitable or at least break even as fast as possible by checking which lander etc converts best and generally have a really deep look into my stats when the first traffic arrives. Then I let it run and monitor, and mostly make decisions after a day.
Ahh, I got that wrong hehe. You were talking about banner impressions to figure out the highest ctr banner
Yeah also around 10k impressions...
I tend to use a calculator (actually one that Julien on these forums pointed me to) - http://statpages.org/confint.html
That lets you know exactly how confident you are of your CTR given number of impressions, number of clicks, and a bunch of other things.
that calculator's sick, stats ftw!
It kicks ass.
You may also find http://visualwebsiteoptimizer.com/ab...ce-calculator/ useful for split-testing landers - the math's rather different, and it's easy to get confused.