Matching in the August AER

Three papers in the August issue of the American Economic Review suggests that the study of matching is thriving.

(2) A Field Study on Matching with Network Externalities

Mariagiovanna Baccara, Ayşe İmrohoroğlu, Alistair J. Wilson and Leeat Yariv

We study the effects of network externalities within a protocol for matching faculty to offices in a new building. Using web and survey data on faculty's attributes and choices, we identify the different layers of the social network: institutional affiliation, coauthorships, and friendships. We quantify the effects of network externalities on choices and outcomes, disentangle the layers of the networks, and quantify their relative influence. Finally, we assess the protocol used from a welfare perspective. Our study suggests the importance and feasibility of accounting for network externalities in assignment problems and evaluates techniques that can be employed to this end. (JEL C78, C93, D62, D85, Z13)

Full-Text Access | Supplementary Materials

(10) Organ Allocation Policy and the Decision to Donate

Judd B. Kessler and Alvin E. Roth

Organ donations from deceased donors provide the majority of transplanted organs in the United States, and one deceased donor can save numerous lives by providing multiple organs. Nevertheless, most Americans are not registered organ donors despite the relative ease of becoming one. We study in the laboratory an experimental game modeled on the decision to register as an organ donor and investigate how changes in the management of organ waiting lists might impact donations. We find that an organ allocation policy giving priority on waiting lists to those who previously registered as donors has a significant positive impact on registration. (JEL C91, D64, I11)

Full-Text Access | Supplementary Materials

(17) The Multi-unit Assignment Problem: Theory and Evidence from Course Allocation at Harvard

Eric Budish and Estelle Cantillon

We use theory and field data to study the draft mechanism used to allocate courses at Harvard Business School. We show that the draft is manipulable in theory, manipulated in practice, and that these manipulations cause significant welfare loss. Nevertheless, we find that welfare is higher than under its widely studied strategyproof alternative. We identify a new link between fairness and welfare that explains why the draft performs well despite the costs of strategic behavior, and then design a new draft that reduces these costs. We draw several broader lessons for market design, regarding Pareto efficiency, fairness, and strategyproofness. (JEL D63, D82, I23)

Full-Text Access | Supplementary Materials

The Economics of Spam by Rao and Reiley

In the latest Journal of Economic Perspectives: The Economics of Spam (open access).

Justin M. Rao and David H. Reiley

"We estimate that American firms and consumers experience costs of almost $20 billion annually due to spam. Our figure is more conservative than the $50 billion figure often cited by other authors, and we also note that the figure would be much higher if it were not for private investment in anti-spam technology by firms, which we detail further on. Based on the work of crafty computer scientists who have infiltrated and monitored spammers' activity, we estimate that spammers and spam-advertised merchants collect gross worldwide revenues on the order of $200 million per year. Thus, the "externality ratio" of external costs to internal benefits for spam is around 100:1. In this paper, we start by describing the history of the market for spam, highlighting the strategic cat-and-mouse game between spammers and email providers. We discuss how th e market structure for spamming has evolved from a diffuse network of independent spammers running their own online stores to a highly specialized industry featuring a well-organized network of merchants, spam distributors (botnets), and spammers (or "advertisers"). We then put the spam market's externality ratio of 100 into context by comparing it to other activities with negative externalities. Lastly, we evaluate various policy proposals designed to solve the spam problem, cautioning that these proposals may err in assuming away the spammers' ability to adapt."

Towards a standard acquisition charge for living donor kidney exchange

The U.S. Agency for Healthcare Research and Quality has awarded a grant to the Alliance for Paired Donation to explore a standard acquisition charge for living kidney donors.

(See this paper for a description of the problem:  Call to develop a standard acquisition charge model for kidney paired donation. Rees MA, Schnitzler MA, Zavala EY, Cutler JA, Roth AE, Irwin FD, Crawford SW, Leichtman AB, Am J Transplant. 2012, Jun; 12(6), 1392-7.)

Here's part of the press release:

 "A pilot project led by The University of Toledo that could increase the number of kidneys available for transplant by the thousands and save U.S. taxpayers millions if implemented nationwide has been funded by the U.S. Agency for Healthcare Research and Quality.

 “Many tests need to be conducted to ensure that a kidney donor and recipient are compatible and that it is safe for the donor to donate,” said Dr. Michael Rees, a University of Toledo Medical Center transplant surgeon and principle investigator of the four-year, $2 million grant. “One of the primary barriers to greater kidney availability is that once an insurance company or Medicare learns that Donor A’s kidney isn’t compatible with Recipient A, they stop funding the tests and no transplant occurs.

“This grant will enable us to create an entity that pays to complete Donor A’s tests, which allows us to discover that Recipient B in another part of the country is compatible,” Rees said. “Once Donor A gives to Recipient B, the insurance company for Recipient B will reimburse the entity for the cost of Donor A’s tests. In a similar way, it may be Donor K or Donor W who ultimately ends up being compatible with Recipient A.”

"Rees estimated that if such a model was expanded nationwide, as many as 1,000 to 3,000 additional kidney transplants would be possible each year.

“The savings to Medicare and insurance companies could reach into the hundreds of millions of dollars due to the elimination of regular treatments like dialysis and other medical efforts for those waiting for an organ,” Rees said.

"To execute the pilot project, UT will partner with the Southwest Transplant Alliance and the Alliance for Paired Donation, an organization founded by Rees to help incompatible kidney donors and recipients find alternative compatible matches. The Alliance for Paired Donation is a Northwest Ohio-based not-for-profit entity that has partnered with more than 80 transplant centers across America to find matches for their patients.

...
"Gold and Rees thanked U.S. Senator from Ohio Rob Portman and Congresswoman Marcy Kaptur for their help in advocating for the value of the grant to those in need of a kidney transplant.
...
"By establishing a standardized charge nationwide for the compatibility testing, removal and transplantation of a kidney, the United States could remove the business disincentive currently in place that inhibits kidney donations across states, across different insurance companies, and between Medicare and Medicaid and private insurers, Rees said.

“This grant will show this idea can work,” Rees said. “The next step will be convincing all parties involved that the concept works and then scaling this project up to the national level using the experience gained to save thousands of lives and millions of dollars every year going forward.”

"In June, Rees and UTMC earned national acclaim for coordinating the first international altruistic kidney donation chain. An earlier chain that began in 2009 has also been covered by People Magazine and published in the New England Journal of Medicine.

How Much Is Your Kidney Worth?

Virginia Postrel uses the recent sentencing in a kidney brokering and sales case to consider How Much Is Your Kidney Worth?

HT: Jonathan Cantor

Altruistic donor chain in NY

A news story about a recent non-directed donor kidney exchange chain at Presbyterian Hospital/Columbia University Medical Center caught my eye for several reasons.

There was a wide range of ages of the donors:
"The series of operation on Wednesday and Thursday, which required 10 separate surgical teams and weeks of coordination, was made up of a series of swaps within a group of men and women between the ages of 23 and 68 and with compatible blood types, all motivated by a mix of compassion and commitment to their loved ones."

The senior surgeon, Dr. Lloyd Ratner, is one of the heroes of kidney transplantation, since he did the first laproscopic live donor nephrectomy, which makes it easier for donors to donate, since smaller incisions are involved than with the surgery that had been commonplace before that.

Lily Kuo, the reporter who wrote the story, notes the important role played by the press:
"After every chain that gets some publicity, there's a flood of potential donors contacting kidney exchange networks and individual transplant centers," Alvin Roth, an economics professor at the Harvard Business School said."

Anatomist and grave robber

His biographer writes about The Beauty of Bodysnatching: Astley Cooper (1768–1841), an English surgeon and anatomist, is remembered for his contributions to vascular surgery and other specialties.

Since dissection was repugnant, cadavers were obtained illegally from grave robbers ("resurrection men").

"in those days to study anatomy required stealing corpses. Cooper went from digging them up himself in the dead of night to running an international network of men who did it for him. As king of the body snatchers he acquired human dead in every state of liquefaction and decay."

Timing of theater reviews

I have a longstanding interest in the timing of transactions (such as unraveling, when transactions become early, or sniping, when they become late, or congestion, when they take a long time, or deadlines). So I read with interest Catherine Rampell's piece on Theater Review Economics, about the timing of theater reviews. (Apparently she's a theater reviewer as well as an economics correspondent.  I guess I won't tell you what I do when not reviewing economics...)

It turns out that when she interviews show producers, one of the answers she gets concerns unraveling (although she discounts this possibility...).


"...as some of you may know, we have an odd little tradition in theater criticism, in that we (almost) never publish a review until after a production’s official opening night. I’ve long wondered about whether it makes good business sense for productions to enforce this embargo.

"While reviews run after opening night, they’re rarely based on a viewing of the actual opening night performance; the curtain generally falls much too late for critics to meet their deadlines for the next day’s paper. Instead, critics usually are invited to attend one of the preview performances after the show has already been “set” or “frozen” — that is, after the director and rest of the creative team have decided not to make any more major changes.

"The time between freezing and opening varies, but it’s generally somewhere from a couple of days to a week.

"I’ve been especially curious about review embargoes lately because summer theater productions usually have very short runs, and should theoretically want reviews published as early as possible — well before the show closes, anyway. Most of the shows I review during the rest of the year have pretty short runs, too, including some productions that last less than two weeks.

"I understand the desire to turn opening night into a big event to magnify press attention, as is done with the openings of big, star-studded movies and their sumptuous red carpets.

"But for a vast majority of theatrical events, little attention is paid to the opening-night parties and such. Even when publications do run photos of the pomp and circumstance of a play’s opening night — if Scarlett Johansson is starring in the show, say — that coverage usually appears in news articles and Us Weekly spreads, not critical reviews.

"Eager for the perspective of those who have money on the line, I called two longtime producers for their thoughts.

"The first was Roger Berlind, a phenomenally successful theater producer who has won 18 Tonys and mounted 80 Broadway shows since 1976, four of which are still running. (Another, “Annie,” opens in November.)

"He noted that when he began producing shows, critics attended on opening night and wrote a review for the late edition of the next day’s paper, since deadlines were often later then. He didn’t sound all too thrilled that the policy had changed.

"Today, he said, producers and press reps encourage the big critics to come a day or two before opening night, even though attending earlier is an option, because the show continues to improve up through the opening night even after the show is set. He said he worried that if critics were able to publish as soon as they saw the show, more of them would rush to see the production as early as possible because “critics are extremely competitive.” That rush would place pressure on the cast and creative team to polish the performances earlier. “Then you’d have to back up the entire process starting with the first day of rehearsal, and I don’t think that would be productive,” he said. “It’s expensive to go through the rehearsal process already.”
**************


I wonder whether the embargo on theater reviews might serve some of the same function that embargoes on news releases do...

Middle school basketball recruiting

Middle School Is Basketball’s Fiercest Recruiting Battleground

"The high caliber of high school basketball in this region and the resulting pressure placed on coaches to win have fostered a fierce recruiting environment focused on players who are much too young to drive anywhere but to the basket.

"Although private schools recruit middle school students in other major metropolitan areas, both openly and discreetly, the minimal regulation of the practice here and the desire to uncover the next Kevin Durant — a product of a Washington-area private school who has blossomed into an N.B.A. star with Oklahoma City — has led to an aggressive pursuit of players beginning with fifth graders.

"All of this, though, is a gamble, done even though coaches realize that, because of teenagers’ natural growth process, players who are stars in sixth grade may never make it past the junior varsity in high school.
...

Priority for organ donation in the UK?

Britain's National Health Service is conducting a survey as part of an assessment of possible changes to its methods of acquiring and allocating organs for transplantation.

NHS considers organ donation shakeup

"The survey asks whether the UK should follow Israel's lead and say that those who are on the organ donor register should get priority if they subsequently need a transplant. "It always seemed to me that fairness is quite a fundamental British value but we have never put that in the context of organ donation," Johnson said.

"The question of presumed consent for organ donation is also raised once more. Only the Welsh assembly government has formally adopted this possibility within the UK, and it plans to legislate in 2015 if its formal consultation goes its way.

"The NHSBT survey asks about extending the recently introduced practice by which the Driver and Vehicle Licensing Centre "nudges" those renewing or updating licences into deciding whether they want to join the donor register to other documents, such as marriage applications or wills. Johnson floated using the new universal credit, the single payment for those seeking work or on low incomes."

The article also speaks of the shortage of deceased donor organs:
"About 1,000 people die in the UK each year because they do not get a transplant, according to NHSBT. Johnson said more people wanted to become donors but the transplant service could not use all the organs they donated. More than 500,000 people die in Britain each year, but only about 3,000 in circumstances where they could realistically become organ donors.
"The reality is you have to die in hospital, on a ventilator, also in the intensive care or emergency department. The number of people dying who are under the age of 75, which is where most of our donors come from, has dropped by about 15% in the last few years. The people who are dying therefore tend to be older, they tend to have more co-morbidity than the rest of the population and, like the rest of the population, they have a tendency to be fatter. Consequently there are a number of people who would like us to use their organs but their organs might not be suitable."


**************

Before we get too excited, note that it's a lot easier to consider changes than to enact them: see my 2008 post on attempts in Britain to move towards presumed consent for organ donation.

Regarding priority for organ donation, Judd Kessler and I have a paper coming out in the August AER:
Kessler, Judd B. and Alvin E. Roth, '' Organ Allocation Policy and the Decision to Donate,'' American Economic Review, forthcoming.

Report from the National Kidney Registry

The American Journal of Transplantation has published (early, online) a report detailing some of the successes of the National Kidney Registry with long, non-simultaneous chains:

Chain Transplantation: Initial Experience of a Large Multicenter Program, by
M. L. Melcher, D. B. Leeser, H. A. Gritsch, J. Milner, S. Kapur, S. Busque, J. P. Roberts, S. Katznelsonf, W. Bry, H. Yang, A. Lu, S. Mulgaonkar, G. M. Danovitch, G. Hil, and J. L. Veale.


"The first 54 chains facilitated 272 transplantations between February 14, 2008 and June 29, 2011.
...
"These first 272 transplants were completed in 40 months and were part of 54 chains that averaged 5.0 transplants long.
...
"In the NKR experience many bridge donors remained motivated and donated months after their intended recipients’ transplantation. One bridge donor even donated more than 1-year afterwards.
...
"The longest chain involved 21 recipients and 21 donors.
...
"There were seven broken chains due to bridge donors becoming unavailable. Unlike traditional paired donation where the consequences of a donor ‘backing-out’ are devastating, in chain transplantation, the next recipient does not suffer ‘irreparable harm’ as they have not lost their willing incompatible donor and can participate in a new exchange when the transplants are carried out sequentially."

The market for marriage proposals...as signals

Need some background as you drop to one knee? There's a market for that...Shock and Aww!

"She had no idea what this was all leading to until Mr. Centner, who had carefully orchestrated this flash mob, took her hand and led her into the circle of dancers.
...
"When asked why some men make a spectacle of their marriage proposal, W. Bradford Wilcox, the director of the National Marriage Project at the University of Virginia, said: “Over-the-top proposals allow men to signal to a future wife, and to family and friends, that they are all in. They are ready to man up, forgo all others and become a responsible husband.”
...
"Which helps explain why, when it comes to proposing, “they want the wow factor,” said Paula Broussard, founder of Dance Mob Nation, a production company based in Los Angeles that has made a specialty out of staging engagements, like the one for Mr. Centner, and other events. Having the aid of a middleman, so to speak, lowers the pressure of having to create a unique will-you-marry-me moment, she said. “They can still have something beautiful, romantic and fun,” she said, “and they don’t personally have to get up and dance — unless they want to.”

"A flash proposal can start at $2,000 for a simple affair, which involves all supporting players — choreographers, videographers, rehearsal rental space and D.J.’s, but Ms. Broussard said that the costs could vary widely because each event is customized. If the would-be groom wants multiple cameras, professional dancers with complex choreography and costumes, the costs can surpass $10,000."

International football (soccer) career paths--the case of Didier Drogba

Simon Kuper in the FT reports on the football career so far of Didier Drogba, which began when he was 5 years old: Didier Drogba is a case study in mobility

" Five-year-old Didier Drogba was moving to France to live with an uncle, a professional footballer.
...
"Last Saturday Drogba, now aged 34, was a match-winner as Chelsea won its first ever Champions League. The Ivorian scored Chelsea’s equalising goal, then netted the decisive penalty. “Drogba’s final”, as it will surely be remembered, proved his last match of eight seasons with Chelsea. He says he is leaving London, and Shanghai Shenhua hopes to sign him. Since that flight from Abidjan, Drogba’s career has become a case study in how a modern professional (footballer or otherwise) should manage mobility.

Video of my talk at Microsoft Research, New England

I gave a talk at MSR New England, to a fairly eclectic audience, so the talk isn't too technical (although it has technical flourishes:).

Random Graph Models in Kidney Exchange - Theoretical Developments and Practical Challenges (the movie), presented at MSR New England, July 25, 2012. The video runs an hour and a half, including the questions at the end.

It gives a quick history of kidney exchange developments, leading up to my recent work on random graphs with Itai Ashlagi, David Gamarnik (who was in the audience) and Mike Rees (who was probably doing a transplant while I spoke). And it ends with some discussion of repugnance--motivated by the laws against buying and selling organs for transplant.

Microsoft has come a long way towards mastering the art of presenting the video and the slides at the same time...you can't see where I'm pointing with the laser pointer or with my hand (since that goes off camera), and when I backtrack on the slides you can seldom see it in the video, but the slides are presented in a way that's mostly well synchronized with the talk (until near the end), and the cameraman doesn't have to choose between the slides and the speaker. (I don't think you can hear the questions though, I'm wearing a microphone, but there wasn't one for the audience members.)  (I wrote the above paragraph after viewing on a large screen: when I viewed the same video on my laptop, and then again on an iPad I had a very different, much less satisfactory experience, and couldn't see the slides at all...:(

Altruistic kidney donors help many, in Science News

Rachel Ehrenberg in Science News reports on long kidney chains: Altruistic kidney donors help many.

"Many people needing kidney transplants have a willing donor, but they can’t take the kidney because it’s not compatible with their blood type or immune system. Paired exchanges, where incompatible donor/recipient pairs swap kidneys with another incompatible pair, is one trick for getting kidneys into hard-to-match patients. Another trick is a donor chain: A person gives a kidney to a clearinghouse or kidney exchange, which can set off a chain of donations.

"Within the kidney transplant community, there’s been an ongoing debate over whether long chains ultimately mean more transplants. “The mathematical question was, are we really transplanting more people?” says Alvin Roth, an expert in game theory and market design at Harvard. “The answer is yes, a lot more.”
...
"It turns out to not be an easy problem. It’s very hard computationally,” says MIT’s Itai Ashlagi, who conducted the analysis along with Roth, MIT’s David Gamarnik, and Michael Rees, a transplant surgeon at the University of Toledo and medical director of the Alliance for Paired Donation, which arranged the first non-simultaneous chain of 10 kidney transplants."

The story also quotes a dissenting voice from Dorry Segev at Johns Hopkins...
**********

Here's the paper:
Ashlagi, Itai, David Gamarnik, Michael A. Rees and Alvin E. Roth, "The Need for (long) Chains in Kidney Exchange," working paper, May 2012.

More on circumcision in Germany

Further developments on the ruling of a German court earlier this summer, banning circumcision.

"German lawmakers have passed a cross-party motion to protect religious circumcision, after a regional court ruled it amounted to bodily harm.

The resolution urges the government to draw up a bill allowing the circumcision of boys.

Germany's main political parties - together with Jewish and Muslim groups - have criticised the ruling by the Cologne court in June.

Chancellor Angela Merkel said it risked making Germany a "laughing stock".

The Cologne ruling involved a doctor who carried out a circumcision on a four-year-old that led to medical complications.

The doctor involved in the case was acquitted and the ruling was not binding. However, critics feared it could set a precedent for other German courts.

Germany's Medical Association told doctors after the ruling not to perform circumcisions.

'Tolerant country' The motion approved on Thursday in the lower house of parliament says the government should "present a draft law in the autumn... that guarantees that the circumcision of boys, carried out with medical expertise and without unnecessary pain, is permitted".

"Jewish and Muslim religious life must continue to be possible in Germany. Circumcision has a central religious significance for Jews and Muslims," it added.

The new law would overrule the decision by the Cologne court.

Ahead of the vote, Foreign Minister Guido Westerwelle said the proposed motion showed that Germany was a "tolerant and cosmopolitan country".

European Jewish and Muslim groups earlier also joined forces to defend circumcision.

An unusual joint statement was signed by leaders of groups including the Rabbinical Centre of Europe, the European Jewish Parliament, the European Jewish Association, Germany's Turkish-Islamic Union for Religious Affairs and the Islamic Centre Brussels.

"We consider this to be an affront [to] our basic religious and human rights," it said.

The BBC's Stephen Evans in Berlin says opinion in Germany about the issue has been mixed, though slightly more Germans were in favour of the ban.

He says that many readers' comments on newspaper websites have indicated anger that this generation of Germans seems to be being constricted in its actions because of the Holocaust."

Angela Merkel intervenes over court ban on circumcision of young boys--Spokesman says right to circumcision must be restored as a matter of urgency, after Cologne court's ruling against practice

"Angela Merkel's spokesman has promised Germany's Jewish and Muslim communities they will be free to carry out circumcision on young boys, despite a court ban that has raised concerns about religious freedom.

"The government said it would find a way around a ban imposed by a court in Cologne in June as a matter of urgency.

"For everyone in the government it is absolutely clear that we want to have Jewish and Muslim religious life in Germany," said Merkel's spokesman, Steffen Seibert.
*********

Ynet covers the story this way: Chancellor told party members she did not want Germany to be 'only country in which Jews cannot practice their rites'
************

 July 19: German MPs vote to protect religious circumcision

"German lawmakers have passed a cross-party motion to protect religious circumcision, after a regional court ruled it amounted to bodily harm.

The resolution urges the government to draw up a bill allowing the circumcision of boys.

Germany's main political parties - together with Jewish and Muslim groups - have criticised the ruling by the Cologne court in June.

Chancellor Angela Merkel said it risked making Germany a "laughing stock".

The Cologne ruling involved a doctor who carried out a circumcision on a four-year-old that led to medical complications.

The doctor involved in the case was acquitted and the ruling was not binding. However, critics feared it could set a precedent for other German courts.

Germany's Medical Association told doctors after the ruling not to perform circumcisions.

...

The motion approved on Thursday in the lower house of parliament says the government should "present a draft law in the autumn... that guarantees that the circumcision of boys, carried out with medical expertise and without unnecessary pain, is permitted".

"Jewish and Muslim religious life must continue to be possible in Germany. Circumcision has a central religious significance for Jews and Muslims," it added.

The new law would overrule the decision by the Cologne court.

Ahead of the vote, Foreign Minister Guido Westerwelle said the proposed motion showed that Germany was a "tolerant and cosmopolitan country".

...

The BBC's Stephen Evans in Berlin says opinion in Germany about the issue has been mixed, though slightly more Germans were in favour of the ban.

He says that many readers' comments on newspaper websites have indicated anger that this generation of Germans seems to be being constricted in its actions because of the Holocaust.

Incentives and privacy

A new paper by three computer scientists and an economist reports on some connections between privacy and incentive compatibility.

MECHANISM DESIGN IN LARGE GAMES: INCENTIVES AND PRIVACY
by
MICHAEL KEARNS, MALLESH M. PAI, AARON ROTH and JONATHAN ULLMAN
July 18, 2012


ABSTRACT
We study the design of mechanisms satisfying two desiderata— incentive compatibility and privacy. The first, requires that each agent should be incentivized to report her private information truthfully. The second, privacy, requires the mechanism not reveal ‘much’ about any agent’s type to other agents. We propose a notion of privacy we call Joint Differential Privacy. It is a variant of Differential Privacy, a robust notion of privacy used in the Theoretical Computer Science literature. We show by construction that such mechanisms, i.e. ones which are both incentive compatible and jointly differentially private exist when the game is ‘large’, i.e. there are a large number of players, and any player’s action affects any other’s payoff by at most a small amount. Our mechanism adds carefully selected noise to no-regret algorithms similar to those studied in Foster-Vohra [FV97] and Hart-Mas-Colell [HMC00]. It therefore implements an approximate correlated equilibrium of the full information game induced by players’ reports.
*********

As I understand it, adding appropriate randomness to regret learning algorithms doesn’t harm their long term equilibration properties, and gives them good privacy properties, which together give them good incentive properties.

Parag Pathak wins Presidential Early Career Award for Scientists and Engineers

It was announced in Washington today that Parag Pathak (who is in Istanbul giving the Shapley Lecture at the World Congress of the Game Theory Society) is one of the winners of the Presidential Early Career Awards for Scientists and Engineers: President Obama Honors Outstanding Early-Career Scientists

"President Obama today named 96 researchers as recipients of the Presidential Early Career Awards for Scientists and Engineers, the highest honor bestowed by the United States Government on science and engineering professionals in the early stages of their independent research careers."


I've had lots of occasions to blog about Parag and his work...

Should there be one kidney exchange or many, and which ones, and when?

The July issue of the Nephrology Times carries a story from the recent American Transplant Congress meetings, at which reports were given by the main kidney exchange networks and transplant centers: In National Paired Donation Pilot, Most Match Offers Declined

Ruthanne Hanto reported on the progress of the Organ Procurement and Transplantation Network (OPTN) Kidney Paired Donation (KPD) Pilot Program run by UNOS.
"The pilot has made about 240 matches since its first run on Oct. 27, 2010, but about 220 of the offers were declined, and only 19 of the matches led to transplantation."

The pilot program hopes to add bridge donors--donors who temporarily end a chain and donate later--at some future time.

In the meantime, the story covers an ongoing debate about whether having multiple kidney exchange networks is a good thing. There's general agreement that, run well, a larger network creates a thicker market which would produce more transplants. And the support of the OPTN, which deals with the nation's deceased donors, gives the pilot program enormous convening power, since they already have working relations with every transplant center in the country.

Nevertheless, the other programs have been vastly more successful in producing transplants, both for patients in general and for the most highly sensitized patients who now make up the majority of those  in kidney exchange networks. (It's hard to come by exact numbers, but we're talking two orders of magnitude--the pilot program so far accounts for about 1% of the kidney exchange transplants to date.) So the story quotes both Ruthanne Hanto and Stanford surgeon Marc Melcher as saying that, for the moment, it would be premature to try to close any of the successful networks down, not least because they are where the innovation is taking place.
(Melcher: “I think at some point most people agree that we need to have a national program. I think really the question is when, and when have we really learned enough about the right way to go.")


The story also quotes Hopkins surgeon Dorry Segev who reaches the opposite conclusion, and would apparently be glad to close down the independent networks: "There's a tremendous amount of competition among the various KPD providers in this country, and this competition is actually hurting the chances for those hardest-to-match patients.”  
*******************


My recent papers which have some bearing on this controversy, in the sense that they are about best practices pioneered in practice by other exchange networks (namely nonsimultaneous chains), are these:

• Ashlagi, Itai, Duncan S. Gilchrist, Alvin E. Roth, and Michael A. Rees, ; ''Nonsimultaneous Chains and Dominos in Kidney Paired Donation -- Revisited,'' American Journal of Transplantation, 11, 5, May 2011, 984-994.
• Ashlagi, Itai, Duncan S. Gilchrist, Alvin E. Roth, and Michael A. Rees, "NEAD Chains in Transplantation," American Journal of Transplantation, December 2011, 11:2780-2781.
• Ashlagi, Itai and Alvin E. Roth, "Individual rationality and participation in large scale, multi-hospital kidney exchange," working paper, January 2011. 
• C. Bradley Wallis; Kannan P. Samy; Alvin E. Roth; and Michael A. Rees, "Kidney paired donation," Nephrology Dialysis Transplantation 2011, doi:10.1093/ndt/gfr155
• Ashlagi, Itai and Alvin E. Roth, "New challenges in multi-hospital kidney exchange," American Economic Review papers and proceedings, May 2012, 102,3, 354-59.
• Rees, Michael A.,  Mark A. Schnitzler, Edward Zavala, James A. Cutler,  Alvin E. Roth, F. Dennis Irwin, Stephen W. Crawford,and Alan B.  Leichtman, “Call to Develop a Standard Acquisition Charge Model for Kidney Paired Donation,” American Journal of Transplantation, 2012, 12, 6 (June), 1392-1397.
• Ashlagi, Itai, David Gamarnik, Michael A. Rees and Alvin E. Roth, "The Need for (long) Chains in Kidney Exchange," working paper, May 2012.

Don't get sick in July...the market for new medical residents

An experienced nurse reflects on the influx of inexperienced new doctors each July in the U.S.: Don't get sick in July

And in England, Thousands of junior doctors have concerns over patient safety: GMC

"One in seven said they had felt forced to cope with clinical problems beyond their competence or experience, according to a survey carried out by the General Medical Council, with a small proportion saying this happened on “a daily basis”.

Hermit Crab Vacancy Chains

From Scientific American:
On a Tiny Caribbean Island, Hermit Crabs Form Sophisticated Social Networks [Video]

In 2009, Lewis and Rotjan surveyed the entire hermit crab population on Carrie Bow Cay. Many crabs were living in shells that were a tight fit or had one too many holes. As they grow, hermit crabs must move into larger shells, so they are always on the lookout for a more spacious dwelling. And an undamaged shell is preferable to a broken one, even if the shells are the same size. Knowing this, the researchers decided to dramatically change the available hermit crab real estate on Carrie Bow Cay. They placed 20 beautifully intact shells that were a little too big for most hermit crabs at various spots around the island and watched what happened.

When a lone crab encountered one of the beautiful new shells, it immediately inspected the shelter with its legs and antennae and scooted out of its current home to try on the new shelter for size. If the new shell was a good fit, the crab claimed it. Classic hermit crab behavior. But if the new shell was too big, the crab did not scuttle away disappointed—instead, it stood by its discovery for anywhere between 15 minutes and 8 hours, waiting. This was unusual. Eventually other crabs showed up, each one trying on the shell. If the shell was also too big for the newcomers, they hung around too, sometimes forming groups as large as 20. The crabs did not gather in a random arrangement, however. Rather, they clamped onto one another in a conga line stretching from the largest to smallest animal—a behavior the biologists dubbed "piggybacking."

Only one thing could break up the chain of crabs: a Goldilocks hermit crab for whom the shell introduced by Lewis and Rotjan was just right. As soon as such a crab claimed its new home, all the crabs in queue swiftly exchanged shells in sequence. The largest crab at the front of the line seized the Goldilocks crab's abandoned shell. The second largest crab stole into the first's old shell. And so on.

No one had ever documented such well-orchestrated shell swapping before, but similar behavior was not unknown. In 1986, Ivan Chase of Stony Brook University made the first observations of hermit crabs exchanging shells in a "vacancy chain"—a term originally coined by social scientists to describe the ways that people trade coveted resources like apartments and jobs. When one person leaves, another moves in. Since then, several researchers—including Lewis and Rotjan—have studied the behavior in different hermit crab species. Some preliminary evidence suggests that other animals use vacancy chains too, including clown fish, lobsters, octopuses and some birds. As Chase explains in the June issue of Scientific American, vacancy chains are an excellent way to distribute resources: Unlike more typical competition, a single vacancy chain benefits everyone involved—each individual gets an upgrade. So it makes sense that hermit crabs and other animals have evolved sophisticated social behaviors to make the most of vacancy chains.

The orderly vacancy chain that Lewis and Rotjan observed is called a synchronous vacancy chain, which is different from an asynchronous vacancy chain in which a lone crab encounters a shell, claims it and leaves behind its old home, which is later seized by a different crab that never interacts with the first animal. As the above video makes clear, however, synchronous vacancy chains are not always civilized affairs. Sometimes crabs fight each other for the best shell or gather in violent groups. And the exchanges often happen extremely quickly. Lewis and Rotjan had to slow down the footage just to see what was happening and it is still difficult to make out: three hermit crabs crowd a large green shell; the largest claims the green shell and the other two swiftly trade up. Lewis thinks the chain would have been more orderly if the crabs were not disturbed by two biologists filming them.

 Sara Lewis and Randi Rotjan 

HT: Benjamin Kay

**************
Update: here's another video https://www.facebook.com/video.php?v=844190408934712 (HT: Yingua He)
***********
And on YouTube (HT Joshua Gans)