Use a ZIP Code Model to Lift Response
"A ZIP code model is an inexpensive tool you can use to increase the profitability of a mailing list. Best of all, you can create a ZIP model using a spreadsheet. ... This model often reveals that ZIP codes in the top one or two deciles (10 percent to 20 percent) usually have a much better than average performance level, while the bottom one or two deciles often drag down average performance."