The majority of Americans support organ donation, but fewer than half of eligible donors actually register. 

Researchers believe this could be because "supporting a good cause doesn't mean people will take action," an American Psychological Association (APA) news release reported. 

The research team believes people who have a positive attitude about donation are still more likely to sign up. 

A 2005 poll found that 95 percent of Americans "support or strongly support" organ donation but only about 40 percent are organ donors. 

"More than 120,000 people in the U.S. were on the waiting list for an organ transplant as of December 2013, and 18 people die each day because they didn't receive a transplantable organ," lead researcher Jason T. Siegel, PhD, of Claremont Graduate University, said in the news release. "We wanted to figure out why there is such inconsistency between peoples' attitudes toward organ donation and donor registration."

The team found that if people felt positively "specifically as signing up as organ donors" they were more likely to register as organ donors. This supports the idea that " specific attitudes" have a larger effect on behavior than "general attitudes." 

"It's a concept researchers need to keep in mind to gather more helpful data to support actions to change behaviors. Research on health issues has had a tendency to rely on global measures of attitude to predict behaviors such as smoking, drinking, taking medication or keeping doctor's appointments," Siegel said. "We should instead measure specific attitudes, whether they're about organ donations or any health-related behavior, from brushing teeth to binge-drinking."

The researchers ran two experiments that included 516 participants, none of which were organ donors. The first group consisted of 358 study subjects who took an online survey and the second group was made up of 158 college students who responded to a written survey in class. 

In the online group "specific attitudes as opposed to general attitudes were 75 percent (10 percent vs. 17 percent), more predictive of organ donor registration." the news release reported. In the college group is was at 150 percent (18.5 percent vs. 42.6 percent). Ten percent of the online group and 13 percent of the college students completed a registration form during the survey. The online participants were asked to indicate whether they agreed or disagreed with statements such as: "I support the idea of organ donation for transplantation purposes," and they completed the sentence "Would registering yourself to be an organ donor ..." with various phrases, such as "be a rewarding act?" or "be a source of anxiety?" The news release reported. 

The students were asked two questions: "In general, how do you feel about organ donation?" and "How do you feel about registering yourself as an organ donor?" The news release reported.Their answers were rated on a scale of negative to positive. 

"Of course, positive attitudes are often not enough on their own to increase donor registration rates. Often what people need is ready access to a registration form," Siegel said.