This is my second time posting this question. I have yet to find anyone who can lend any kind of real insight. Can you help?

Some have argued, simplistically, that the “core” response for a direct mail publication should be the number of weeks it takes to achieve 80% of TOTAL response (following the simplistic 80/20 heuristic).

Others have suggested that the “core” response rate should be time it takes to get to 90% to 100% of the total response (which could take infinitely long).

Frequently, when looking at response data, it can take as many weeks to get from 80% to 90% as it did to get from 0% to 80%. This “velocity” of response varies with each direct mailing

My thought is that velocity should be an important factor in this analysis, but I’m ignorant about how to use it. Even 80% may not be appropriate depending upon how slow the response is.

What is the best way to quantitatively define what a “core” response rate is, regardless of the velocity of response?