The question of Direct Marketing has gone through several revolutions. I remember when I was young, the national association was the Direct Mail Marketing Association. Direct mail went back into the 1800's, it was the proven, measurable and testable.
More than a few years ago, I was in a ad agency... I was the 'direct mail' guy. They asked me, "What is the difference between what we do and direct marketing?" Great question ... So I wrote this article: Why Direct Marketing is Misunderstood. Excellent, check it out. Here is another version in Target Marketing.
In my YouTube Video on Direct Marketing I mentioned a cover test - here it is, can you see the difference?
The image on the left pulled 40% better than the cover on the right. It was a 600,000 piece test and not even a letter of copy was different in the two catalogs.