One last comment, this is assuming you have legit stats to begin with. I mean in the first month you should have a certain # of downloads given the amount of impressions and clicks you send, which should correlate to a certain number of signups. If you send a lot of traffic and you don’t see any signups then you don’t need any more than 1 month to make a decision here as long as you have a large enough sample to know if this program even converts or not.
John