Although most Americans say they support the idea of organ donation, less than half of eligible donors ever register, according to a recent study reported by the Imperial Valley News.

Research published by the American Psychological Association suggests this may be because "supporting a good cause doesn't mean people will take action." However, they note that people are more likely to sign up if they have positive attitudes specifically about registering as a donor.

A Gallup poll conducted in 2005 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 of Claremont Graduate University said in a news release. "We wanted to figure out why there is such inconsistency between peoples' attitudes toward organ donation and donor registration."

Siegel and colleagues found that people who said they felt positive specifically about signing up as an organ donor  were much more likely to register than if they simply said they strongly support the general idea of organ donation. This finding illustrates a psychological principle that specific attitudes are more likely to predict 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 study was funded by the U.S. Department of Health and Human Services' Division of Transplantation, Imperial Valley News reported.