In the past three months, I’ve been invited to like a cause on Facebook 49 times. Each time, I’ve dutifully clicked through—it’s an easy way to show my support. Since Giving Tuesday was this week, it seemed like the perfect time to like more causes and join more giving groups.

Not so fast. Research on “slacktivism” reveals that supporting a cause on Facebook actually reduces the odds that we will contribute to it. Once we’ve shown our support and earned the status associated with joining a cause, we feel less obligated to follow through with a meaningful contribution to that cause. As Seth Meyers said on Saturday Night Live, “Look, if you make a Facebook page we will ‘like’ it—it’s the least we can do. But it’s also the most we can do.”

Instead of asking people to like your cause on Facebook, evidence supports five better ways to promote giving:

1. Invite Commitments to Specific Acts of Giving

In Influence, psychologist Robert Cialdini reports extensive evidence that once people have chosen to give their time and energy to a cause, it becomes part of their , and they’re more likely to do it again. The Effective movement does this beautifully, asking people to pledge to donate a portion of their income to charity.

2. Make the Behavior—Not the Signature—Public

The slacktivism studies showed that when people signed a petition confidentially, they were more inclined to give. The private signature meant that they were committing to do good, rather than just look good. But we shouldn’t give up on going public altogether: we just need to shine the spotlight on the action rather than the commitment.

In a clever experiment, behavioral economist Dan Ariely and colleagues asked people to press as many X-Y pairs on their keyboard as possible in five minutes, and promised to donate money to the Red Cross for each pair typed. On average, people typed just over 500 pairs. But when they learned that other participants would find out about their pairs, they put in 74% more effort, typing an average of 900 pairs. By making the specific act of giving visible, people actually have to put in the effort to look good.

3. Highlight the Right Reason to Give

A large university sent emails inviting donations from nearly a thousand alumni who had never given a cent in their lives. The emails highlighted two different reasons to give: “Giving is your chance to make a difference in the lives of students, faculty, and staff” (benefit to others) or “Alumni report that giving makes you feel good” (personal benefit). Dan Feiler, Leigh Tost, and I were surprised to find that the two reasons were equally effective: about 6.5% of alumni donated in each case.

Since they appeal to different types of people, we thought it would be optimal to combine them. We were wrong. When we featured the two reasons together, the odds of donations were cut in half, to below 3%. Mixing different reasons made it salient that a persuasive attempt was occurring, and people were less motivated to give. New research suggests that it’s particularly ineffective to present more than three reasons, which dilutes the message—and people can just choose the least compelling reason as an excuse not to give. Researchers Suzanne Shu and Kurt Carlson report that “Three charms but four alarms.”

4. Encourage Reflection on Past Contributions

In one experiment, Jane Dutton and I found that after listing specific ways that they had helped others in the past week, the likelihood that people would donate to an earthquake relief fund more than doubled, from 21% to 46%. In another experiment, after fundraisers wrote about a few ways that they had helped others, they increased their hourly calls by 29% over the next two weeks.

When we reflect on our past contributions, we gain in our capabilities to give and reinforce our identities as givers. They need to be specific, though: research shows that after people write about themselves in broad terms as caring, generous, or kind, they are about two and a half times less likely to donate to a charity of their choice. As I explained in Give and Take, they told themselves, “I’m a giving person, so I don’t have to donate this time.”

5. Humanize the Need

Imagine seeing a picture of a starving seven-year-old from Africa—either a girl (Rokia) or a boy (Moussa), and being asked to donate money for food, , and medical care. It turns out that people give at equal rates to Rokia and Moussa, but there was a third group who saw both Rokia and Moussa. Would they give more or less?

We should give more when two children are in need, rather than one. Yet as with combining multiple reasons, presenting multiple recipients backfired. Participants gave 19% less when two children were in need. As philosopher Peter Singer writes in The Life You Can Save, “An individual need tugs at our emotions.”

The same pattern was visible on Kiva, where people give micro-loans as small as $25 to help people in the developing world escape poverty and start businesses. When researchers studied over 289,000 loans to more than 23,000 borrowers, lenders loaned significantly less money to groups of borrowers than individual borrowers. “Lending is less likely as borrower group size increases,” the researchers write.

is most powerful when it’s directed toward one identifiable person. When a single person is in need, we think “I can make a difference.” When many people are in need, giving is only a drop in the bucket, so should I really bother? In the words of Mother Teresa, “If I look at the mass I will never act. If I look at the one, I will.”

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Adam Grant is a Wharton professor and the author of Give and Take, a New York Times and Wall Street Journal bestseller about how acts of helping others drive our success. Follow him on LinkedIn at www.linkedin.com/influencer/profadamgrant and on Twitter @AdamMGrant