Given this shortage of organs, why don’t more people donate?

It’s a touchy question, something non-donors aren’t necessarily keen to answer. But experts say there is a large disparity between the number of people who say that they support organ donation in theory and the number of people who actually register. In the U.K., for example, more than 90 percent of people say they support organ donation in opinion polls, but less than one-third are registered donors. What keeps well-intentioned people from ultimately donating is something that academics, doctors, and organ-donation activists are trying to figure out.

In a recent literature review, researchers at the University of Geneva examined several social and psychological reasons why people choose not to donate, either by not registering as an organ donor during their lives, or electing not to donate the organs of their next of kin.

The study cites mistrust in the medical field and lack of understanding about brain death as major barriers to donation. A 2002 study in Australia, for example, illustrates the controversy surrounding brain death. Some participants indicated that they wouldn’t donate the organs of their next of kin if his or her heart were still beating, even if they were proclaimed brain-dead.

Studies have also shown that the less people trust medical professionals, the less likely they are to donate. The mistrust can come from personal experience—one study in New York showed, for example, that next of kin who perceived a lower quality of care during a loved one’s final days were less likely to consent to donation—or from misconceptions about how the medical community treats registered organ donors.

“There are a lot of people who subscribe to the belief that if a doctor knows you are a registered donor, they won’t do everything they can to save your life,” says Brian Quick, an associate professor of communication at the University of Illinois.

More than half of people, one study shows, have gotten information regarding organ donation from TV, so it makes sense that researchers are concerned with how fictional medical dramas can influence our attitudes toward medical professionals (a topic The Atlantic covered in August).

Quick and his colleagues have studied how watching Grey’s Anatomy can influence people’s attitudes toward the medical community. “We found that heavy viewers of the show saw Grey’s Anatomy as realistic, meaning that they felt the images and the stories were realistic. And the more realistic they saw these stories, the more likely they were to buy into medical mistrust.”

Religion is another factor that repeatedly comes up in research. While many religions consider organ donation an act of love, some research has shown that Catholics are less likely to donate than other religious groups, despite the Vatican’s official position in favor of it. It seems that this is due to a belief in the afterlife and the concern for maintaining body integrity.