Given the level of debate that surrounds the use of “Merry Christmas” versus “Happy Holidays,” online retailers probably have an easier time deciding which products to put on sale at this time of the year than what greeting to use in their marketing.

The prevailing theory is to use catch-all phrases like “Happy Holidays” or “Season’s Greetings” to cover the bases for all religious holidays celebrated in the US toward the end of December. For graphics, companies either stick to winter motifs (a subtle reference to Christmas, even for those living in snow-free climates) or bright color schemes.

But is the generic approach really the best approach?

Conversion Voodoo, a provider of landing page optimization services, was inspired last December by a Wall Street Journal article to test the power of the phrase “Merry Christmas” for one of its clients. On behalf of a large retailer, they set up a test using identical emails, save for three different subject lines and the carrying over of these themes to the email body; the subject lines tested were “Merry Christmas,” “Happy Holidays,” and “Merry Christmas & Happy Holidays.”

The “Merry Christmas” subject line trounced the other test cells, generating a click-through rate (5.47%) that was nearly double what each of the other two test versions produced. In addition, open rates were noticeably lower for the test segments that received the generic or the hedge-your-bets subject lines.

The results of this test made me think of a direct marketing twist on a popular adage: When in doubt, test it out.

An equally important conclusion that can be drawn from Conversion Voodoo’s exercise is that it’s always good to challenge your assumptions. Why not let the market decide?

Wishing you happy testing, so you get more of another word that starts with a “c”—conversions!