3. Select a cross-section of any list for both the control and test groups. Test panels must be selected the same way.
4. Mail dates must be the same for all panels.
5. Be careful when using dollar minimums to qualify the offer.
In summary, avoid conditioning your customers to expect an offer every time they buy. Guard against a decline in response rates from over-promoting an offer. And be careful how you use order minimums. Use offers carefully and have a purpose for every offer you make.
Stephen R. Lett is president of Lett Direct, a catalog consulting firm specializing in circulation planning, forecasting and analysis. He can be reached at (302) 541-0608 or via his Web site: www.lettdirect.com.