Does a decrease in the number of traffic fatalities increase live kidney donation?

Over at Economic Logic, the Economic Logician reviews an article, The Effect of Traffic Safety Laws and Obesity Rates on Living Organ Donations by Jose Fernandez and Lisa Stohr. It finds that a decrease in availability of deceased donor organs (through an increase in helmet and seatbelt laws) elicits some increase in live donor kidney donation.

Here's the abstract, followed by EL's summary.

Abstract: This paper uses variation in traffic safety laws and obesity rates to identify substitution patterns between living and cadaveric kidney donors. Using panel data from 1988-2008, we find that a 1% decrease in the supply of cadaveric donors per 100,000 increases the supply of living donors per 100,000 by .7%. With respect to traffic safety laws, a national adoption of partial helmet laws is estimated to decrease cadaveric donors by 6%, but leads to a 4.2% increase in the number of living donors, or a net effect of 1.8% decrease in the supply of kidney donations. The recent rise in obesity rates is estimated to increase living donor rates by roughly 18%. Lastly, we find evidence that increases in disposable income per capita is associated with an increase in the number of non-biological living donors within a state, but is not found to have an effect on biological donor rates.

And here is EL's summary:

"There are times where you really wonder why authors would even think that some variables could be correlated and how they then come up with a story that can explain this statistical relationship coming from seemingly nowhere. The paper by Jose Fernandez and Lisa Stohr is one of these.To quote their abstract, "this paper uses variation in traffic safety laws and obesity rates to identify substitution patterns between living and cadaveric kidney donors." Despite reading this sentence ten times, I could not make any theoretical sense of it. But reading through the paper, a good story can be made. Tightening traffic safety laws reduces the number of fatalities, and thus the number of cadaveric organ donors. An increase in obesity increases the demand for organs, in particular kidneys. Thus one can instrument for supply and demand using these measures. With this in mond, one can then study how variations in the supply of supply of cadaveric organs (which are of poor value) and demand can motivate living donors to come forward, as they trade off the usefulness of their donation with the personal harm it will inflict upon them. Fernandez and Stohr fiand that donors respond indeed to cadaveric supply and to the increase in demand due to obesity."