"Almost any question can be answered cheaply, quickly, and finally, by a test campaign. And that's the way to answer them -- not by arguments around a table. Go to the court of last resort -- the buyers of your product." -- Claude Hopkins, "Scientific Advertising," 1923.
Eighty years later, direct and database marketing still thrive on this basic premise: Test-Measure-Refine:
It's usually best to focus only on key factors, especially when you are just beginning to test:
Testing does not always make economic sense, like when your mailing quantity or mailing frequency is low. List tests are always a good idea. We think the Test-Measure-Refine loop is as valuable today as it was 80 years ago when Hopkins described it.