How large do my test mailings need to be?

Answered by Brendan Talty

How large do my test mailings need to be?

Good question, but just a bit off target. It's not the mail quantity that matters when you want to ensure that results are valid for rollout consideration, it's the number of RESPONSES.

Consider this: A catalog client wanted to make sure that the results of a price test would be significant enough to roll out to the entire base. Their response averaged 12% over the years (true, believe it or not). So how many packages to mail? While there are computer models that will compute the required test quantity for you, I use a rule of thumb that 300 responses per test panel is enough to make a test significant at the 95% confidence level (the industry standard in direct marketing).

So...300 divided by 12% yields a mail quantity of 2,500. Now go ahead and plug in your expected response rate to determine what your test quantity should be next time you're in the mail.
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