Here's an example. Last year I sent a 700 piece mailing to local prospects. The variable I tested was the ink color of the return mailing address on the envelope. labels (yep, I'm that anal). Half (350) of the labels were printed in blue, the other half in black. The offer I was making was the same in both envelopes.
Forty (40!!!) more people took advantage of the offer with the blue address label. That's a rediculous difference in response and rediculously important information. Why? Because now I know to expect a higher response to future offers when I send them with blue return address labels!
I'm not stopping there though. What if a red return address lable is more effective than blue?
For my next mailing, that's what I'm gonna test. If blue pulls better than red, I know I've got something here. If red pulls better than blue, that's great too because blue works great already! So then I'll test red against another color, and so on.
What else can you test?
You name it, you can test it. And when you use the results to your advantage it's the best way in marketing to make every dollar you spend do the work of $2 or more. And that's what it's all about!
Doing an email campaign to promote Winter Camp? Test two subject lines against each other to see which gets the best response. For example:
Subject Line # 1: "Sign up now for Winter Camp"
Subect Line #2: "Save 10% Off Winter Camp. Enroll Now!"
If one of the emails pulls significantly better than the other, you know you've got a winner. Just be sure everything else in both emails is exactly alike, because if you change any other variable (even a picture or single word), you won't be comparing apples to apples and your results will not be true.