EVERY YEAR, WHEN my favorite radio station stages its dreaded on-air fund-raiser, I hold my donation for the morning when they announce the two-for-one matching grant. This year it never materialized. Turns out, lots of charities are dropping these fat matches, and it s not just due to the vacillating economy: New research shows that a dollar-for-dollar match is just as effective as the two-for-one. Most people donate because they want to feel that warm glow, says John List, the University of Chicago economist who conducted the study. And a bigger match doesn t necessarily make for a warmer glow.

For decades many nonprofits relied on intuition and experience when crafting charitable solicitations. But this holiday season, be prepared for more sophisticated lures. Academics have taken a shine to the topic, and their field experiments have yielded surprising findings that nonprofits can use to create more powerful appeals.

Experimentation isn t new, of course. The largest nonprofits have long relied on direct-marketing experts who test everything from envelope colors to font sizes, says Olivia Smith, a senior VP at BKV, an Atlanta consultancy whose clients include The Salvation Army and the March of Dimes. She s found that photos of sick children outperform photos of healthy ones, while extra inserts (brochures, newsletters) increase the length of engagement, leading to more donations. The perfect letter, meanwhile, creates a sense of anxiety by describing a terrible problem before providing an easy solution: Send a check! You ve given the donor a way to ease the tension you ve created, says Smith.

Test results can be comical. A first-class stamp on the outside envelope generates higher response rates then a postal mark; a return envelope featuring several little stamps adding up to 44 cents performs best of all, because donors assume some sweaty volunteer made a big effort.

If it sounds like many donors make decisions based on emotion and irrelevant information, that s about the size of it. In one widely noted experiment, researchers with Save the Children found donors who were given stats about a famine in Ethiopia gave 25 percent more when they were also provided a photo of Rokia, a 7-year-old who faces a threat of severe hunger or even starvation. That s not surprising. But here s the kicker: They gave 66 percent more than that when they got the photo and story line without the famine data. Statistics, it seems, reduce empathy and interest in giving, says Christopher Olivola, coeditor of The Science of Giving: Experimental Approaches to the Study of Charity.

Researchers discovered a similar phenomenon in an experiment conducted with ChildFund International. As you d expect, potential donors gave more when they were told the fund had an excellent rather than a poor efficiency ratio. But the highest response came from donors who were given no efficiency information at all. People give less when they re thinking analytically, says Princeton psychology professor Danny Oppenheimer.

Donors also act like sheep. In an experiment with Sierra Club, researchers found donations increased 23 percent when prospects were told a major donor had made a big contribution. Rightly or wrongly, we assume a rich philanthropist has inside information about the quality of a charity. People like to invest with a winner, says List. And when it comes to door-to-door fund-raising, never underestimate the power of a pretty face. Researchers raising funds for East Carolina University found that a good-looking woman at the door could double the frequency of donations. And blondes raised 65 percent more than brunettes.

The upshot? It s best not to act on impulse. While a compelling appeal might stir your interest in a cause, the nonprofit with the best marketing doesn t necessarily have the best programs, Olivola notes. But perhaps it s not such a bad thing that charities are getting better at pulling our heartstrings. After all, he says, maybe, in the end, the most rational person is the person who keeps the money for himself.