Many Times a Short Letter Will Do Just Fine
But, sorry, it's not that simple. You need to look at the direct marketing application.
Long letters do work better in order generation - meaning mail-order, subscription selling and fundraising - when you actually have to close the sale ... when you are asking the reader to open his wallet and make a financial commitment. To be successful in order generation, you need to give the reader all the information, answer all the questions and spell out all the details of your offer. And, yes, long letters give you the space to do that.
But in lead generation, all you are asking the reader to do is send back a reply card, perhaps with a few questions answered. Your offer is generally something free - a white paper, an information kit, a seminar - so you don't need to provide nearly as much information. A one- or two-page letter and reply card would usually do it. And in retail traffic building, restaurants and dry cleaners don't need a four-page letter. A postcard would work just fine for them.
Bob McCarthy, McCarthy & King Marketing Inc.,