Incentivizing people to register as organ donors has long been a topic of debate.

That's because offering incentives, financial or otherwise, for organ donor registrations raises ethical and legal questions. To this point, organ donations have been secured through entirely voluntary means.

A person either willfully volunteers to register as an organ donor, making his or her wishes known, or the family of a deceased person voluntarily decides to donate their loved ones' organs.

Even so, there are far more people in need of organs than there are organs available. Every day, 18 people die waiting for an organ transplant and finding ways to increase the number of available organs is of utmost importance to saving lives.

The donor-priority rule was developed as a potential way to encourage organ donor registrations. It works like this. If a person signs up to be an organ donor, the potential donor will receive a higher priority on the transplant list if he or she ever needs an organ transplant.

However, this arrangement brings about an unintended consequence. People who are at risk of needing an organ transplant are more likely to register as organ donors. And generally speaking, people who need organ transplants are sick.

New research published in the Institute for Operations Research and the Management Sciences journal Management Science pinpoints a potential solution. A freeze period must be instituted along with the donor-priority rule. That is, donors would not be eligible to advance higher on the transplant list until they had been on registry for a specific period of time.

Researchers from Johns Hopkins University, Carnegie-Mellon University and the University of Texas at Austin tested the hypothesis by creating a simulated organ market using artificial intelligence. The study used data from the Organ Procurement and Transplantation Network to create the hypothetical market.

"When the donor-priority rule and freeze-period are imposed together the average quality of donated organs is restored. The freeze-period makes it more time-consuming to get on the list deterring people from using the organ-donation system to solely get to the top of the list if they need to, whereby increasing the amount of unhealthy donations," said Tinglong Dai, a professor in the Carey Business School at Johns Hopkins University.

"When a stronger incentive is given to high-risk individuals it results in reduction of organ quality," Dai said. "Such problems can outweigh the potential gain for the registry. These people are pressured into donating because they need a donation themselves and there is a slim chance they'll get it if they don't register."

The simulation showed the biggest benefit of the two-pronged incentive approach to be an increased patient lifespan. In one test, an organ recipient lived 18 years longer than if the organ had not been available. The years were valued at $50,000 per year. Donations from sick donors added only 10 years to the recipient's life expectancy.

"By adding the freeze period restriction, it helps rebalance the incentive structure and can guarantee a boost in organ supply without compromising organ quality. The change would boost social welfare by $235 million a year," Dai said.