Integration of online and direct mail fundraising has been a staple topic of development conferences for at least five years now. So it’s time to separate the results from the hype.

Yes, of course you should seek to integrate your mail and online programs, and the larger the programs, the more upside for integration. Of course, you want to enable your supporters to donate by whatever channel they choose for a given gift—the BRE, the donation page on your site, or plain unmarked bills delivered to your door.

While online giving has grown significantly over the last five years, most donors still give by mail. Just 9% of donors came in online in the most recent evaluation of 12 national organizations, but they account for 21% of new-donor revenue because of much higher gift levels. The online donors are younger and have higher household income (because they’re working, not retired).

Over the last three years, the donorCentrics ™ Internet Benchmarking program that my firm, Donordigital, has worked on with Target Analytics has shown that up to 25% of online-acquired donors make at least one gift online, but that few mail-acquired donors give online. When mail donors do migrate to online giving, their gifts are larger. And when online donors give in the mail, they give smaller gifts.

Some of the giving difference is certainly age—most online donors are over 60, many over 70, and these folks are less likely to give on. Habit also seems to be a factor: The longer a mail-acquired donor is on your file, the less likely she will make an online gift. However, these numbers are averages, and your file may differ, especially if you have a younger mail file (such as a group like Human Rights Campaign) or if earthquakes, hurricanes, or other high-profile emergencies motivate your mail donors to go online to give.

As you probably know by now, online donors have higher lifetime value than mail donors, mainly because their average gifts are so much higher. Multi-channel donors are even more valuable. But even mail donors with email addressees on file who have not given online are more valuable, either because the email messages they receive motivate them to give more in the mail or because the donors who offer you their email addresses care more about you. (What about donors whose e-mail addresses you have appended? We don’t have the data, but it could be they’re more affluent and/or younger than those for whom you can’t find an email address.)

So what should you do?

Nick Allen is Co-founder and Chief Strategy Officer of Donordigital, the online fundraising, marketing, and advertising company.