Monday, January 22, 2018

Pursuing Global Kidney Exchange in Rome: photos

I was recently in Rome, where a substantial group gathered (see below) to further the possibilities of Global Kidney Exchange (GKE). Part of our efforts were focused on presentations to a January 15-16 Meeting of the EU Competent Authorities on Organ Donation and Transplantation, Co-Chaired by the European Commission..

You can see a photo of Mike Rees beginning his talk, with the names of various co-conspirators.
Finally, there's good coffee in Rome. I recommend the famously good Sant Eustachio.





So far, the EU competent authorities haven't issued any statement.

Sunday, January 21, 2018

The number of organ donors in Germany has fallen to its lowest level in 20 years.

Rosemarie Nagel draws my attention to this article in Der Spiegel on transplantation in Germany:



Transplantation
Wieso werden in Deutschland so wenige Organe gespendet?
Die Zahl der Organspender in Deutschland ist auf den niedrigsten Stand seit 20 Jahren gesunken. Woran liegt das? Und wie kann man einer Spende zustimmen - oder sie ablehnen? Der Überblick.

Google translate renders it as: Transplantation
Why are donated so few institutions in Germany?
The number of organ donors in Germany has fallen to its lowest level in 20 years. Why is that? And how can you agree to a donation - or reject it? The overview.

Friday, January 19, 2018

Bob Wilson, Paul Milgrom and Dave Kreps win the Carty Award



Game theory at Stanford:)


Here's the press release from the National Academy of Science

David M. Kreps, Stanford University Graduate School of Business, Paul R. Milgrom, Stanford University Department of Economics, and Robert B. Wilson, Stanford University Graduate School of Business, will receive the 2018 John J. Carty Award for the Advancement of Science.


"Kreps and Wilson provided a framework, known as sequential equilibrium, for modeling dynamic effects in economics. All three of the award winners, together with other collaborators and in particular D. John Roberts, employed these techniques to model and study reputation and collusion, both of which have broad applications in macroeconomics, industrial organization, and labor economics.
Later, the entire modern telecommunications industry arose out of an auction format developed by Milgrom and Wilson, along with Preston McAfee, for the 1994 radio spectrum auctions by the Federal Communications Commission. The simultaneous ascending auction format, in which each bidder can bid for multiple licenses over a series of rounds so long as it remains “sufficiently active,” has since been used around the world to allocate hundreds of billions of dollars’ worth of wireless licenses. Variations of the format have also been applied to numerous other industries, including electricity markets and various commodity markets.  
The three award winners, with collaborators and alone, have contributed broadly to other topics in economics: Kreps has done foundational work in choice theory and financial market theory; Milgrom, in the theories of market microstructure and the principal-agent problem; and Wilson, in nonlinear pricing and utility regulation, as well as the foundations of dynamic equilibria.
The John J. Carty Award for the Advancement of Science is awarded every two years, to recognize noteworthy and distinguished accomplishments. In 2018 the award is presented in the field of economics. The award is presented with a medal and a $25,000 prize."

Thursday, January 18, 2018

Evolution of dating apps: OK Cupid requires mutual consent for messaging

Slate reports (last month):
OkCupid Users Have Long Had to Put Up With Unwanted Messages. That's About to Change
"OkCupid announced a big change to its messaging system in an email to users on Friday afternoon. Starting next week, the email said, “Only the people you like or have responded to will remain in your messages. Messages from people you're not interested in, or people you haven't liked yet, will be moved to their profile.”
"This shift will bring the platform more in line with other online dating platforms, such as Tinder and Bumble, on which users can’t message one another at all until both have shown interest in the other. The new OkCupid way won’t be quite so strict—users can still send messages to whomever they want, though those messages will only appear in the recipients’ mailboxes if they indicate that they like the sender—but engineers hope it will help seed more connections while filtering out some messages that will never get a response."

Wednesday, January 17, 2018

Analytic approaches to allocating organs for transplants

Two recent items:

Adapting a Kidney Exchange Algorithm to Align with Human Values
by Rachel Freedman, Jana Schaich Borg, Walter Sinnott-Armstrong, John P. Dickerson, Vincent Conitzer

Abstract:
The  efficient  allocation  of  limited  resources  is  a  classical problem in economics and computer science. In kidney exchanges,  a  central  market  maker  allocates  living  kidney donors to patients in need of an organ. Patients and donors in kidney exchanges are prioritized using ad-hoc weights decided on by committee and then fed into an allocation algorithm that determines who get what—and who does not. In this paper, we provide an end-to-end methodology for estimating weights of individual participant profiles in a kidney exchange.  We first elicit from human subjects a list of patient attributes they consider acceptable for the purpose of prioritizing patients (e.g., medical characteristics, lifestyle choices,and  so  on).  Then,  we  ask  subjects  comparison  queries between  patient  profiles  and  estimate  weights  in  a  principled way from their responses. We show how to use these weights in kidney exchange market clearing algorithms. We then evaluate the impact of the weights in simulations and find that the precise numerical values of the weights we computed matter little, other than the ordering of profiles that they imply.However, compared to not prioritizing patients at all, there is a significant effect, with certain classes of patients being (de)prioritized based on the human-elicited value judgments.
**************

And

How analytics and machine learning can aid organ transplant decisions
by Dimitris Bertsimas and Nikolaos Trichakis

"MIT Sloan and Massachusetts General Hospital have developed an analytics tool to help doctors in deceased-kidney acceptance decisions. The model aims to calculate the probability of a patient being offered a deceased-donor kidney of a certain quality level within a specific time frame (three, six, or 12 months), given their individual characteristics. Using machine learning, it looks at 10 years of data and millions of prior decisions to estimate a patient’s waiting time in the context of a current active organ offer until the time to the next offer for a higher quality kidney."

Tuesday, January 16, 2018

Welfare effects of limiting the number of interviews by Beyhaghi and Tardos

Here's a new paper on a subject that is coming up in a number of the markets that I keep an eye on:

Effect of Limited Number of Interviews onMatching Markets
by Hedyeh Beyhaghi and Eva Tardos

Abstract. We study outcome of two-sided matching between prospective medical residents who can only apply to a limited number of positions and hospitals who can interview only a limited number of applicants and show non-intuitive effects in the matching outcomes. We study matching size as our notion of efficiency, and show when the number of interviews is limited, a market with limited number of applications achieves a higher efficiency compared to a market with no limit. Also we find that a system of treating all applicants equally (setting the same limit for their number of applications), is more efficient rather than allowing a small set to apply to one more/less position. This comparison results in a scallop-shape figure 2 that shows expected size of matching with respect to expected number of applications. Finally we show that limiting number of interviews does not always hurt efficiency of matching markets and can improve social welfare in certain cases. 

Monday, January 15, 2018

Spain continues to lead in deceased donation

I'm in Rome to talk today with the 28 EU Competent Authorities on Organ Donation and Transplantation about ways of increasing living donation through kidney exchange, by easing barriers at borders.

In the meantime, Spain remains a model for deceased donation:
Spain breaks organ transplant and donor records again
"The country's National Transplant Organisation (ONT) said 2017 saw a total of 5,259 transplant operations performed beating 2016's record of 4,818 transplants.

The majority were kidney and liver transplants.

Spain also boasts a much higher average of organ donors with 46.9 donors per million people in 2017, compared with 43.9 per million in 2016 and 39.7 in 2015.

The EU average is just 19.6 donors per million and the US average is 26.6 per million."

Sunday, January 14, 2018

Applications and interviews for medical residencies

The computerized clearinghouse for the NRMP medical match solves the congestion problem for new doctors when it comes time to make offers, acceptances and rejections. But electronic applications make it easier to apply for lots of places, and this is coming to seem like a problem in both the resident match and in the later-career fellowship matches.

Residency Placement Fever: Is It Time for a Reevaluation?
Gruppuso, Philip A. MD; Adashi, Eli Y. MD, MS
Academic Medicine
Issue: Volume 92(7), July 2017, p 923–926

Abstract: The transition from undergraduate medical education to graduate medical education (GME) involves a process rooted in the final year of medical school. Students file applications through the Electronic Residency Application Service platform, interview with residency training (i.e., GME) programs from which they have received invitations, and generate a rank-ordered preference list. The National Resident Matching Program reconciles applicant and program rank lists with an eye towards matching students and GME programs. This process has effectively served generations of graduating medical students. However, the past several decades have seen an intensification of the residency placement process that is exemplified by an inexorable increase in the number of applications filed and number of interviews accepted and attended by each student. The authors contend that this trend has untoward effects on both applicants and departments that are home to GME programs. Relevant information in the peer-reviewed literature on the consequences and benefits of the intensification of the residency placement process is scant. The authors address factors that may contribute to the intensity of the residency placement process and the relative paucity of data. They propose approaches to reverse current trends, and conclude that any reevaluation of the process will have to include the generation of outcome data to afford medical educators the opportunity to explore changes in an evidence-based manner.
..............

"In part, the intensification phenomenon is borne out by the aforementioned growth in ERAS-associated traffic. In the eyes of many, this “new normal” draws on the widespread perception that a successful match in highly competitive disciplines is contingent on the filing of applications with a large proportion of the relevant GME programs. For example, in 2015, senior U.S. medical students applied, on average, to 73 of the 163 orthopedic surgery programs and 47 of the 105 neurological surgery programs (based on data extracted from the AAMC 8 and the NRMP 9,10). What is more surprising is that even less competitive disciplines may now be seeing an ever-growing flood of applications. This contention is supported in part by recent observations according to which GME programs in nearly all disciplines have seen a marked increase in their application traffic. For example, the percentage of pediatric GME programs to which graduating U.S. medical students have applied on average increased from 9.8% to 13.7% during the five-year interval from 2010 to 2015.10 For internal medicine GME programs, the corresponding figures are 4.9% to 6.0%.8–10 In making these decisions, students appear to be keeping their own counsel against the advice of medical school advisers and mentors advocating moderation."
...
"First, consideration should be given to the possibility of coordinating the timing of the interviews and of the Match across all disciplines and GME programs, including the “early match” disciplines of ophthalmology and plastic surgery.32 Consolidation along these lines would address the disruption of fourth-year scheduling, thereby offering educators greater flexibility in designing the fourth-year curriculum. Implementing such changes will not be easy given the longevity, familiarity, and comfort associated with the extant construct. Voluntary action on the part of the relevant professional associations will be required should a realignment of current schedules ever come to pass. Second, reducing if not capping the number of interviews per student would go a long way towards stemming the time and resource drain on both applicants and GME programs. This, too, is not going to be easy given the near-universal presumption that “more is better” and the notion that the times in effect demand such. In this context, consideration might be given to a tiered “screen and schedule” system wherein initial online interviews with many or all eligible applicants would be followed by a limited set of on-site interviews with a select group of “finalists.” As envisioned, this approach, widely used in both the public and the private sectors, stands to rationalize the current residency placement process while maintaining its fundamental premises of excellence and compatibility. Limiting the final on-site interviews to a select number of candidates will also give rise to palpable economies of scale that are likely to be welcomed by applicants, GME programs, and medical schools alike."

Saturday, January 13, 2018

Radio interview on The Quarterly Report

I was interviewed Wednesday by Craig Hafer and Mike Faust on their radio show The Quarterly Report, starting with questions about my book Who Gets What and Why and moving on to market design generally, and then to Shotokan karate.   You can hear the conversation here:


You can also download the show as an mp3 audio file here:
https://weeushows.podbean.com/e/dr-alvin-roth-on-feedback/

Friday, January 12, 2018

Bichler on market design: textbook from Cambridge U. Press


Martin Bichler has a new textbook on market design, focused on auctions and linear programming:

Market Design A Linear Programming Approach to Auctions and Matching

  • Date Published: December 2017 

Thursday, January 11, 2018

Videos from the 2018 AEA Posters

This year the AEA meetings continued the tradition of having lots of poster presentations, and of videotaping some of the authors.
You can find those here: 2018 AEA Poster Videos (and the collection from previous years, which right now also includes just 2017 when we started this here: AEA Poster Session Videos).

You can go directly to each of the 2018 poster presentations at the links below:


Ann Owen on gender diversity on bank boards

January 9, 2018
How does having more women on a board affect bank performance?


Antonio Alonso Arechar on the role of honesty in cooperation

January 10, 2018
Does "cheap talk" help people work together?

Carola Binder on how gas prices are tied to consumer inflation expectations

January 10, 2018
How should monetary policymakers respond to energy price fluctuations?


Dennis Bonam on the stability of monetary unions

January 9, 2018
Can monetary unions come back from unstable times?


Elmer Li on assessing school quality

January 10, 2018
Is student mobility a better measure of school quality than test scores?


Jim Marrone on the black market for antiquities

January 9, 2018
How do economists study archaeological looting?


Lei Gao on mortgage discrimination to same-sex loan applicants

January 9, 2018
How do lenders treat homosexual borrowers differently?


Lucy Xiaolu Wang on how health IT reduces opioid-related deaths

January 10, 2018
How can prescription monitoring programs be more effective?


Seth Gershenson on the impact of same-race educators

January 9, 2018
What impact does having a same-race teacher have on long-term student performance?


Shaikh Eskander on how Bangladeshi farmers adapt to natural disasters

January 9, 2018
How do farmers use the land rental market to mitigate the effects of climate change?


Sriya Anbil on emergency lending in the Great Depression

January 9, 2018
How can we identify "bad banks"?

Wednesday, January 10, 2018

Do organ donors have a right to donate?

Here's a case that makes clear that some donors really wish to become donors, in this case deceased donors. The story is from the Canadian Broadcasting Service news:
Organ donation changes dying for those getting medically assisted death
People who have chosen to die with medical assistance are often the best candidates for donation

"When ALS diminished Brian Wadsworth's quality of life, he asked for medical assistance in dying. Organ donation was the natural next choice. And while the decision came with logistical challenges and ethical concerns, his loved ones say he never looked back."

Tuesday, January 9, 2018

Video from the AEA meetings (including my presidential address)

If you missed the AEA/ASSA meetings that just finished in Philadelphia, you can still hear some of the talks.

Here's mine (it's about an hour, but afterwards you'll know everything I know):
AEA Presidential Address - Marketplaces, Markets and Market Design
Alvin E. Roth, introduced by Olivier Blanchard
View Webcast

Update: it turns out the AEA website included this picture...


And here are the other videos:

2018 AEA Annual Meeting Webcasts of Selected Sessions

View Webcasts of selected sessions from the Annual Meeting in Philadelphia on January 5-7, 2018! (compliments of the AEA):

January 5, 2018

Climate Policy and Trade
Presiding: Mar ReguantRegulating Mismeasured Pollution: Implications of Firm Heterogeneity for Environmental Policy Eva Lyubich, Joseph Shapiro, and Reed Walker
How Trade-sensitive are Energy-intensive Sectors? Carolyn Fischer and Alan Fox
Measuring Leakage Risk Meredith Fowlie and Mar Reguant
Discussants: Matilde Bombardini, Thibault Fally, and Teresa Fort
View Webcast
TrumpEconomics: a First Year Evaluation
Presiding: Dominick Salvatore
The Effects of Policy Uncertainty Olivier BlanchardThe Impact of the Trump Tax Reforms Martin FeldsteinWhat's Lacking in Trumpean Economic Policy Edmund PhelpsTrump and Globalization Joseph E. StiglitzContinuing Relevance of Secular Stagnation Lawrence H. SummersDiscussant: Dominick Salvatore
View Webcast
AEA/AFA Joint Luncheon - Liquidity and LeveragreRaghuram Rajan, introduced by David Scharfstein
View Webcast
New Measures of the EconomyPresiding: Betsey Stevenson
Estimating Changes in Well-being Using Massive Online Choice Experiments Erik Brynjolfsson, Felix Eggers, and Avinash Gannamaneni
Measuring Social Progress: Evidence from Advanced Economies Daniel Fehder, Scott Stern, and Michael E. Porter
Using Online Prices to Measure Standards of Living Across Countries Alberto Cavallo, W. Erwin Diewert, Robert Feenstra, Robert Inklaar, and Marcel Timmer
Internet Rising, Prices Falling: The Era of e-Commerce and its Macroeconomic Implications Austan Goolsbee and Pete Klenow
Discussants: Carol Corrado, Betsey Stevenson, Dennis Fixler, and Leonard Nakamura
View Webcast
AEA Richard T. Ely Lecture: Competition, Equilibrium, Freedom, and PaternalismDavid Laibson
View Webcast


January 6, 2017

Central Bank Communications
Presiding: Andrew HaldaneFuture of Monetary Policy Communications Alan Blinder
Central Bank Forward Guidance and the Signal Value of Market Prices Hyun Song Shin and Stephen MorrisCentral Bank Communications and the General Public Michael McMahon and Andrew HaldaneDiscussants: Ricardo Reis, Michael Ehrmann, and Refet Gurkaynak
View Webcast
Global Inequality and Policy
Presiding: Emmanuel SaezThe Elephant Curve of Global Inequality and Growth Facundo Alvaredo, Lucas Chancel, Thomas Piketty, Emmanuel Saez, and Gabriel Zucman
From Communism to Capitalism: Private Versus Public Property and Inequality in China and Russia Filip Novokmet, Thomas Piketty, Li Yang, and Gabriel Zucman
Applying Generalized Pareto Curves to Inequality Analysis Thomas Blanchet, Bertrand Garbinti, Jonathan Goupille-Lebret, and Clara Martinez-Toledano
Extreme Inequality: Evidence from Brazil, India, the Middle-East, and South Africa Facundo Alvaredo, Lydia Assouad, Lucas Chancel, and Marc Morgan
Discussants: Thomas Blanchet, Lucas Chancel, Emmanuel Saez, and Li Yang
View Webcast
AEA Nobel Laureate Luncheon Honoring the 2016 Nobel Laureates in Economics: Oliver Hart (Harvard University) and Bengt R. Holmstrom (Massachusetts Institute of Technology)Presiding: Olivier Blanchard
Luigi Zingales 

Daron Acemoglu
View Webcast
Economic Consequences of Artificial Intelligence and Robotics
Presiding: Erik Brynjolfsson
Demographics and Robots Daron Acemoglu and Pascual Restrepo
What Can Machines Learn, and What Does It Mean for the Occupations and Industries? Erik Brynjolfsson, Tom Mitchell, and Daniel Rock
Linking Advances in Artificial Intelligence to Skills, Occupation, and Industries Rob Seamans and Edward W. Felten
Human Judgement and A.I. Pricing Joshua Gans, Avi Goldfarb, and Ajay AgrawalDiscussants: Benjamin Jones, Shane Greenstein, Susan Helper, and J. Miguel Villa-Boas
View Webcast
AEA Awards Ceremony
Presiding: Olivier Blanchard
View Webcast

Monday, January 8, 2018

Medical school admissions in Germany

Sven Seuken and Stephanie Wang point me to these stories:

Germany: Selection process for medical students deemed partly unconstitutional
Germany's top court has ruled that the current method universities use to allocate places for medical studies violates equal opportunity laws. The federal government is to regulate the criteria used for offering places.

"Under the current system, German universities are able to apply what was known as the 20-20-60 rule for prospective medical students. Twenty percent of places are allocated to students with the very best overall marks in the final school exams, a selection process generally referred to as the numerus clausus. Often students with marks as high as 1.2 (the equivalent of a 3.9 GPA in the US) would not be guaranteed a place.

"A further 20 percent of places go to students who had been previously been placed on a waiting list.

"The remaining 60 percent are chosen based on various criteria determined by the individual universities — a system the judges found to be unfair.

"Three universities — Aachen, Bonn and Düsseldorf — base their selection only on the average school grades, while a number of other institutions make prospective students have an interview. Lawmakers must now work to lift these discrepancies.

"Applicants who are not accepted in the first selection round can be put on a waiting list for up to seven years, according to some estimates. The court also ordered officials to work on shortening those waiting times.


"The claim was taken to court by two applicants who had achieved a grade of 2.0 and 2.6, but hadn't been admitted to medical school after being on the waiting list for eight and six years respectively. "
**************

Here's a more detailed article in German
Medizin-NC vor dem Bundesverfassungsgericht
Sie können doch nicht warten, bis alle grau sind
(G Translate: Medical NC in the Federal Constitutional Court
You can not wait until all are gray)

Sven Seuken writes:
"The judges criticized, in particular:
@1: even if your GPA is high enough to get into some school, because of the limitation to a list length of 6 (where you rank universities), you might get unlucky and get into no school. That's unfair.

@2: If you get into a school "by waiting long enough", your waiting time to get a spot at a university might be 7.5 years. That is considered "dysfunctional". However, I have no idea if they have a better system in mind.

@3: Some universities only use the GPA as their selection criterion for category 3. The judges criticized this, and said that at least one more criterion must be used."

Sunday, January 7, 2018

More on the repugnance of selling art, if you're an art museum

In Philadelphia:
La Salle plan to sell museum masterpieces stuns art community

"La Salle University, which has struggled to plug a projected deficit in recent years, plans to sell 46 pieces of art from its prized museum collection to help fund teaching and learning initiatives in its new strategic plan, officials said Tuesday...

Approved by the school’s board of trustees and announced by university president Colleen M. Hanycz, the decision “is a strategic and good use of our assets,” university spokeswoman Jaine Lucas said. “We are doing what we feel is in the  interest of our students.”
It follows similar steps by other universities around the country in recent years to help stem financial woes — although some schools that have sold or attempted to sell art have faced challenges.
At Brandeis University in Massachusetts, a plan to close its museum and sell its art was reversed after backlash from students and faculty and legal action. Randolph College in Virginia was roundly criticized for its decision to sell a George Bellows painting worth more than $25 million.
The same controversy could follow the decision at La Salle, a 3,200-student Catholic university in Philadelphia’s Logan section, whose collection composes one of the most highly regarded university museums in the region. Just hours after the announcement, members of the local art community began questioning the decision."


"The process of selling art, known as deaccessioning, is a fraught one for museums; major professional organizations like the American Alliance of Museums condemn the sale of art to pay for expansions, physical repairs or ongoing expenses, as opposed to using the proceeds for the acquisition of other works or, perhaps, the care of a collection.

At times, government agencies that oversee nonprofit institutions have intervened to halt sales.

In 2009, for instance, the attorney general’s office in Massachusetts conducted a detailed review of Brandeis University’s unexpected announcement that it would shore up its struggling finances by selling all of the works––including those by Robert Rauschenberg, Jasper Johns, Andy Warhol and Roy Lichtenstein––held by its Rose Art Museum, one of the most important collections of postwar art in New England.

Later four of the museum’s benefactors sued to stop any art sales.

That lawsuit and the attorney general’s investigation were both resolved in 2011, with Brandeis announcing that it had “no aim, plan, design, strategy or intention to sell any artwork donated to or purchased by” the school for the museum and that the Rose museum will remain a “university art museum open to the public.”

Saturday, January 6, 2018

The open culture of academic economics

I'll be delivering the Presidential Address at the American Economic Association meetings in Philadelphia today, with a paper to follow later this year. I plan to talk and write about marketplaces, which I think are understudied parts of markets. And I think that market design has a bright future, both as a kind of engineering economics that can help people in very concrete ways, and as a way to shed new light on markets and how they work.

But I'm also finding this a moment to take a look backward as well as forward. Personally, looking backward fills me with feelings of gratitude: not only to my family and to my teachers and advisers, to my wonderful students and coauthors; but also to the profession of economics and all of you economists who made me welcome, although economics isn’t a subject in which I ever received any degree.

During my professional career I have participated in at least three academic insurrections, which brought game theory into economics, and experimental and behavioral economics, and most recently market design.  There have been other revolutions as well, in econometrics and computation and access to large linked data sets among others. And these revolutions have come about largely because economists are on the whole enthusiastic about finding new ways to explore the large swath of human behavior that makes up economics.

I hasten to add that this welcoming of new ideas isn't magical, or even immediately apparent. Like raising children, it's a slow process while it's going on, but it becomes clear in retrospect how fast it actually is. Paper by paper (referee report by referee report) academic economics can feel pretty conservative and resistant to change. But when you look at things at the time scale of decades, economics has opened up to new ideas very fast.

We've also been welcoming to intellectual immigrants: to people as well as ideas. I'm hardly alone among economists of my generation who don't have degrees in economics. A bunch of us rode in on the wave that brought game theory into economics. Not every discipline is as open to new ideas or new people.  This openness is something to treasure, gratefully and vigilantly.

Looking ahead, I hope we can continue to nurture this openness to both ideas and people.  Exciting things are happening in other disciplines (computer science, biology...), and there's plenty of room for cross fertilization between disciplines, as well among the diverse points of view and diverse people already "inside" economics.

Economics is still an early-stage science, so it's an exciting time to be an economist. There's lots of progress we still need to make, it's important for the world that we do so, and there are some indications of fruitful paths to follow.  I'm looking forward with substantial optimism.

Friday, January 5, 2018

Black markets in guns without serial numbers

The WSJ has the story:

The Rise of Untraceable ‘Ghost Guns’
An emerging black-market gun-making industry lets buyers bypass background checks and gun regulations, authorities say

"The number of these weapons in the U.S. is unknown. Because the guns bear no serial numbers, the Bureau of Alcohol, Tobacco, Firearms and Explosives is unable to track them. Serial numbers and gun registration play a key role in police and government investigations, allowing officers to trace a weapon’s history and owners.

"Ghost guns appear to be most prevalent in California, where there are restrictions on assault weapons that make it difficult to buy guns that are available in other states. But the firearms have been seized in criminal investigations in other states, including Arizona, Maryland, New York and Texas.
...
"“It went from being a niche group of people that were into the gun culture that were the ones making them for themselves,” said Mr. Barlowe. “Now, they’ve become so commonplace we’re buying them from 17-year-old gang-members on the street.”

"The starting point for building a ghost gun is an “unfinished receiver,” a metal or polymer piece that houses the firing mechanism. It can be purchased online without a background check, because the ATF doesn’t classify the part as a firearm.
...
"“There is a loophole under federal law that allows an individual to make a firearm,” said  Justin Lee, a federal prosecutor in Sacramento who has handled several ghost gun cases. “That loophole only extends to that person. The person breaks the law as soon as they are transferring that firearm.”
...
"The prevalence of online retailers and YouTube instructional videos has given ghost guns a boost, according to Mr. Barlowe. He said illicit gun dealers can buy parts for an AR-15 style rifle for about $700, put in a few hours of sweat equity, and sell it on the street for $1,000 to $2,000.
...
"Gun-owners distrustful of registering their firearms with the government also are customers. “Unserialized, Unregistered” is the slogan for GhostGuns.com, which sells handgun kits, unfinished receivers, and other items. Kyle Martin, president of Ghost America LLC, which runs the site, said customers “want to enjoy their complete freedom as American citizens.”