TUESDAY, May 8 (HealthDay News) -- Incentives such as gift cards, T-shirts and coupons encourage more people to donate blood, a new study finds.

Researchers analyzed data from 14,000 blood drives involving 500,000 donations in the United States, along with evidence from a field experiment. They found that incentives led to a 15 percent to 20 percent rise in the number of people taking part in blood drives.

Incentives did not change people's key reasons for donating blood but did pull donors away from other blood drives that did not provide incentives, according to the study, which was published in a recent issue of the American Economic Journal: Economic Policy.

"It's a pretty remarkable increase [in donor numbers]," study co-author Nicola Lacetera, an assistant professor of strategic management at the University of Toronto's Rotman School of Management, said in a university news release.

Other studies have produced similar findings.

"One study at a time, we believe we are building pretty robust evidence that there is a positive response to rewards," Lacetera said.

About 30 percent to 40 percent of American Red Cross blood drives offer some type of incentive. Fewer than 10 percent of people in the United States and Canada donate blood, however, and blood shortages are the norm.

More information

The U.S. Food and Drug Administration has more about blood donation.