Alex Tabarrok of Marginal Revolution (marginalrevolution.com) stirred up a debate in the blogosphere by asking who really benefits when he gets a flu shot.

“People who have the flu spread the virus so getting a flu shot not only reduces the probability that I will get the flu it reduces the probability that you will get the flu,” he writes. “In the language of economics the flu shot creates an external benefit, a benefit to other people not captured by the person who paid the costs of getting the shot. … Since a large fraction of the benefits of the flu shot, perhaps even a majority of the benefits, go to other people and not to the person paying the costs, the number of people who get a flu shot in the United States is well below the efficient level.”

On how to encourage more people to get vaccinated, Mr. Tabarrok offers the following: “I only got the shot because, as you well know, I’m altruistic. I care about you. But do send your checks, that will help.”

Lynne Kiesling (knowledgeproblem.com) takes Mr. Tabarrok’s final suggestion seriously, and disagrees: “This is the crucial point to remember whenever anyone starts talking about tax or subsidy policies to ‘internalize externalities’: at the margin, the greatest beneficiary of Alex’s action is Alex. If the marginal benefit to him of getting the shot is larger than the marginal cost, then he’ll do it, even if we don’t have some elaborate scheme of subsidies to compensate him for the benefit he generates for us. If his desire to prevent illness in himself and in his close circle is high enough, he’ll do it, and any payment we make to him at the margin … might not change his behavior.” The case amounts to an “irrelevant externality,” she says, in which case “a system of payments provides nothing more than a wealth transfer without changing the actual amount of the beneficial behavior that occurs.” Daniel Hall of Common Tragedies (commontragedies.wordpress.com) objects, saying, “surely someone out there is on the margin about a vaccination decision, and it would make sense if we could target a subsidy at them. Off-hand I would guess that this group would include the poor and uninsured … and the young, single, and socially mobile, since they are less likely to have compelling reasons to act selflessly. And, let’s face it,” he adds, “they are frequently lazy.”

FREE MARKETS AND EVOLUTION At Cafe Hayek (cafehayek.typepad.com), Don Boudreaux waxes philosophical about curious inconsistencies in the ways American liberals and conservatives utilize the concept of “undesigned order” in their respective arguments. He draws the admittedly simplified comparison: “Modern American conservatives (at least those in the freemarket camp) insist that physical and biological reality must be the product of conscious design and creation, but these conservatives also readily accept that productive social orders—such as markets—can, and do, emerge undesigned and unplanned.” On the other hand, “Modern American ‘liberals’ (at least those who aren’t religious in the conventional sense) insist that productive social orders must be the product of conscious design and creation” while readily accepting that biological orders can emerge spontaneously through the process of evolution.