Success Rate on Direct Mail?

[Julie Groth]

What is your success rate on your direct mail campaigns? Please notice that I'm asking about success rate, not response rate. :)

How many pieces do you need to mail out to actually close on a deal?

I realize that there are many variables, like who you are mailing to, the quality of the list, etc...but generally speaking. Say, I want to close on 1 house per month, then how many letters/postcards should I plan to send?