Paul Milgrom, Nobel Laureate

By Tyler Cowen

Most of all this is a game theory prize and an economics of information prize, including game theory and asymmetric information.  Much of the work has had applications to auctions and finance.  Basically Milgrom was the most important theorist of the 1980s, during the high point of economic theory and its influence.

Here is Milgrom’s (very useful and detailed) Wikipedia page.  Most of his career he has been associated with Stanford University, with one stint at Yale for a few years.  Here is Milgrom on scholar.google.com.  A very good choice and widely anticipated, in the best sense of that term.  Here is his YouTube presence.  Here is his home page.

Milgrom, working with Nancy Stokey, developed what is called the “no trade” theorem, namely the conditions under which market participants will not wish to trade with each other.  Obviously if someone wants to trade with you, you have to wonder — what does he/she know that I do not?  Under most reasonable assumptions, it is hard to generate a high level of trading volume, and that has remained a puzzle in theories of finance and asset pricing.  People are still working on this problem, and of course it relates to work by Nobel Laureate Robert Aumann on when people should rationally disagree with each other.

Building on this no-trade result, Milgrom wrote a seminal piece with Lawrence Glosten on bid-ask spread.  What determines bid-ask spread in securities markets?  It is the risk that the person you are trading with might know more than you do.  You will trade with them only when the price is somewhat more advantageous to you, so markets with higher degrees of asymmetric information will have higher bid-ask spreads.  This is Milgrom’s most widely cited paper and it is personally my favorite piece of his, it had a real impact on me when I read it.  You can see that the themes of common knowledge and asymmetric information, so important for the auctions work, already are rampant.

Alex will tell you more about auctions, but Milgrom working with Wilson has designed some auctions in a significant way, see Wikipedia:

Milgrom and his thesis advisor Robert B. Wilson designed the auction protocol the FCC uses to determine which phone company gets what cellular frequencies. Milgrom also led the team that designed the 2016-17 incentive auction, which was a two-sided auction to reallocate radio frequencies from TV broadcast to wireless broadband uses.

Here is Milgrom’s 277-page book on putting auction theory to practical use.  Here is his highly readable JEP survey article on auctions and bidding, for an introduction to Milgrom’s prize maybe start there?

Here is Milgrom’s main theoretical piece on auctions, dating from Econometrica 1982 and co-authored with Robert J. Weber.  it compared the revenue properties of different auctions and showed that under risk-neutrality a second-price auction would yield the highest price.  Also returning to the theme of imperfect information and bid-ask spread, it showed that an expert appraisal would make bidders more eager to bid and thus raise the expected price.  I think of Milgrom’s work as having very consistent strands.

With Bengt Holmstrom, also a Nobel winner, Milgrom wrote on principal-agent theory with multiple tasks, basically trying to explain why explicit workplace incentives and bonuses are not used more widely.  Simple linear incentives can be optimal because they do not distort the allocation of effort across tasks so much, and it turned out that the multi-task principal agent problem was quite different from the single-task problem.

People used to think that John Roberts would be a co-winner, based on the famous Milgrom and Roberts paper on entry deterrence.  Basically incumbent monopolists can signal their cost advantage by making costly choices and thereby scare away potential entrants.  And the incumbent wishes to be tough with early entrants to signal to later entrants that they better had stay away. In essence, this paper was viewed as a major rebuttal to the Chicago School economists, who had argued that predatory behavior from incumbents typically was costly, irratoinal, and would not persist.

The absence of Roberts’s name on this award indicates a nudge in the direction of auction design and away from game theory a bit — the Nobel Committee just loves mechanism design!

That said, it is worth noting that the work of Milgrom and co-authors intellectually dominated the 1980s and can be identified with the peak of influence of game theory at that period of time.  (Since then empirical economics has become more prominent in relative terms.)

Milgrom and Roberts also published a once-famous paper on supermodular games in 1990.  I’ve never read it, but I think it has something to do with the possible bounding of strategies in complex settings, but based on general principles.  This was in turn an attempt to make game theory more general.  I am not sure it succeeded.

Milgrom and Roberts also produced a well-known paper finding the possible equilibria in a signaling model of advertising.

Milgrom and Roberts also wrote a series of papers on rent-seeking and “influence activities” within firms.  It always seemed to me this was his underrated work and it deserved more attention.  Among other things, this work shows how hard it is to limit internal rent-seeking by financial incentives (which in fact can make the problem worse), and you will see this relates to Milgrom’s broader work on multi-task principal-agent problems.

Milgrom also has a famous paper with Kreps, Wilson, and Roberts, so maybe Kreps isn’t going to win either.  They show how a multi-period prisoner’s dilemma might sustain cooperating rather than “Finking” if there is asymmetric information about types and behavior.  This paper increased estimates of the stability of tit-for-tat strategies, if only because with uncertainty you might end up in a highly rewarding loop of ongoing cooperation.  This combination of authors is referred to as the “Gang of Four,” given their common interests at the time and some common ties to Stanford.  You will note it is really Milgrom (and co-authors) who put Stanford economics on the map, following on the Kenneth Arrow era (when Stanford was not quite yet a truly top department).

Not what he is famous for, but here is Milgrom’s paper with Roberts trying to rationalize some of the key features of modern manufacturing.  If nothing else, this shows the breadth of his interests and how he tries to apply game theory generally.  One question they consider is why modern manufacturing has moved so strongly in the direction of greater flexibility.

Milgrom also has a 1990 piece with North and Weingast on the medieval merchant guilds and the economics of reputation, showing his more applied side.  In essence the Law Merchant served as a multilateral reputation mechanism and enforced cooperation.  Here is a 1994 follow-up.  This work paved the way for later work by Avner Greif on related themes.

Another undervalued Milgrom piece is with Sharon Oster (mother of Emily Oster), or try this link for it.  Here is the abstract:

The Invisibility Hypothesis holds that the job skills of disadvantaged workers are not easily discovered by potential new employers, but that promotion enhances visibility and alleviates this problem. Then, at a competitive labor market equilibrium, firms profit by hiding talented disadvantaged workers in low-level jobs.Consequently, those workers are paid less on average and promoted less often than others with the same education and ability. As a result of the inefficient and discriminatory wage and promotion policies, disadvantaged workers experience lower returns to investments in human capital than other workers.

With multiple, prestigious co-authors he has written in favor of prediction markets.

He was the doctoral advisor of Susan Athey, and in Alex’s post you can read about his auction advising and the companies he has started.

His wife, Eva Meyersson Milgrom, is herself a renowned social scientist and sociologist, and he met her in 1996 while seated next to her at a Nobel Prize dinner in Stockholm.  Here is one of his papers with her (and Ravi Singh), on whether firms should share control with outsiders.  Here is the story of their courtship.