Godspeed to Sarah Murnaghan and Javier Acosta, both of whom are at Children's Hospital of Philadelphia suffering from the debilitating effects of cystic fibrosis. U.S. District Judge Michael Baylson granted them relief recently by allowing each to join the waiting list for an adult lung. This prompted the Organ Procurement and Transplantation Network to create a special appeal and review system to hear cases in which children need access to adult organs.

While Javier is still waiting, Sarah received a transplanted lung from an adult donor just days ago. But if we really want to swell the number of available hearts, lungs, livers, and corneas, there is a more obvious and expansive solution.

We need to start assuming that most people wish to be organ donors, while allowing those who object to opt out easily. The current policy in the United States is the opposite: an opt-in system.

An analysis in the Harvard Business Review five years ago noted that different organ donation policies in two neighboring, culturally similar countries, Germany and Austria, produced dramatically different results. In Germany, where citizens must opt into the donor pool, only 12 percent of the population had done so. In neighboring Austria, where all citizens are placed in the donor pool by default — although they can easily opt out — the share of the population in the pool was 99.98 percent.

One of the coauthors of that article, Columbia Business School Prof. Eric J. Johnson, has made this issue the focus of his academic study for the last two decades. A cancer survivor, Johnson underwent a stem-cell transplant in which he served as his own donor. The experience made him appreciate his own fortune while recognizing the obstacles faced by those who need donations of bone marrow and other stem cells, which are in short supply for certain blood types.

Now Johnson believes that the key to increasing donations is to change the default option — the automatic selection made in the absence of a decision to the contrary. Such defaults are part of everyday life. When a car-rental company provides insurance unless you decline it, that is a default. Every time you click "next" as part of a quick installation of software on your computer, you are accepting a default.

In a 2003 analysis published in the journal Science, Johnson and coauthor Daniel G. Goldstein cited a study showing that while 85 percent of Americans support organ donation, less than half personally decide to become potential donors, and fewer still (28 percent) sign a donor card. Why? Johnson believes the discrepancy is attributable to the default assumption that most of us do not wish to donate, which requires us to opt in.

He suggests three reasons for the widespread failure to opt in. First, people are lazy. Second, making nondonation the default is seen as an implied endorsement of that position. Third, there is what economists call the "endowment effect," which describes our tendency to attach more value to what we already possess.

"If I am a donor, I don't want to change that state, because the warm glow of being a donor goes away," he explained. "On the other hand, if I'm not a donor, and you ask me to change, I start thinking about what it would be like to have my cadaver ... organs taken. So people are naturally drawn to the features of the object they are about to give up. That's a subtle but important psychological point."

In a 2004 article published in Transplantation, Johnson and Goldstein documented the power of defaults with a local example: Pennsylvania and New Jersey auto insurance defaults introduced in the early 1990s. New Jersey drivers had a limited right to sue by default, while Pennsylvania drivers had full litigation rights. While 79 percent of New Jersey drivers said they preferred limited litigation rights, 70 percent of Pennsylvania drivers said they preferred an unrestricted right to sue. Given that residents of neighboring states came to such opposite conclusions, the default option was clearly influencing their views.

"If you take a case like organ donation, you have to have a default," Johnson said. "The question is, What's the right default?" The way to ensure that other families don't experience the pain felt by the Murnaghans and Acostas is to significantly expand the pool of available organs. If we're serious about it, it's time to embrace an opt-out system.