The 2017 Nobel: Richard Thaler

A true surprise this morning: the behavioral economist Richard Thaler from the University of Chicago has won the Nobel Prize in economics. It is not a surprise because it is undeserving; rather, it is a surprise because only four years ago, Thaler’s natural co-laureate Bob Shiller won while Thaler was left the bridesmaid. But Thaler’s influence on the profession, and the world, is unquestionable. There are few developed governments who do not have a “nudge” unit of some sort trying to take advantage of behavioral nudges to push people a touch in one way or another, including here in Ontario via my colleagues at BEAR. I will admit, perhaps under the undue influence of too many dead economists, that I am skeptical of nudging and behavioral finance on both positive and normative grounds, so this review will be one of friendly challenge rather than hagiography. I trust that there will be no shortage of wonderful positive reflections on Thaler’s contribution to policy, particularly because he is the rare economist whose work is totally accessible to laymen and, more importantly, journalists.

Much of my skepticism is similar to how Fama thinks about behavioral finance: “I’ve always said they are very good at describing how individual behavior departs from rationality. That branch of it has been incredibly useful. It’s the leap from there to what it implies about market pricing where the claims are not so well-documented in terms of empirical evidence.” In other words, surely most people are not that informed and not that rational much of the time, but repeated experience, market selection, and other aggregative factors mean that this irrationality may not matter much for the economy at large. It is very easy to claim that since economists model “agents” as “rational”, we would, for example, “not expect a gift on the day of the year in which she happened to get married, or be born” and indeed “would be perplexed by the idea of gifts at all” (Thaler 2015). This type of economist caricature is both widespread and absurd, I’m afraid. In order to understand the value of Thaler’s work, we ought first look at situations where behavioral factors matter in real world, equilibrium decisions of consequence, then figure out how common those situations are, and why.

The canonical example of Thaler’s useful behavioral nudges is his “Save More Tomorrow” pension plan, with Benartzi. Many individuals in defined contribution plans save too little, both because they are not good at calculating how much they need to save and because they are biased toward present consumption. You can, of course, force people to save a la Singapore, but we dislike these plans because individuals vary in their need and desire for saving, and because we find the reliance on government coercion to save heavy-handed. Alternatively, you can default defined-contribution plans to involve some savings rate, but it turns out people do not vary their behavior from the default throughout their career, and hence save too little solely because they didn’t want too much removed from their first paycheck. Thaler and Benartzi have companies offer plans where you agree now to having your savings rate increased when you get raises – for instance, if your salary goes up 2%, you will have half of that set into a savings plan tomorrow, until you reach a savings rate that is sufficiently high. In this way, no one takes a nominal post-savings paycut. People can, of course, leave this plan whenever they want. In their field experiments, savings rates did in fact soar (with takeup varying hugely depending on how information about the plan was presented), and attrition in the future from the plan was low.

This policy is what Thaler and Sunstein call “libertarian paternalism”. It is paternalistic because, yes, we think that you may make bad decisions from your own perspective because you are not that bright, or because you are lazy, or because you have many things which require your attention. It is libertarian because there is no compulsion, in that anyone can opt out at their leisure. Results similar to Thaler and Benartzi’s have found by Ashraf et al in a field experiment in the Philippines, and by Karlan et al in three countries where just sending reminder messages which make savings goals more salient modestly increase savings.

So far, so good. We have three issues to unpack, however. First, when is this nudge acceptable on ethical grounds? Second, why does nudging generate such large effects here, and if the effects are large, why doesn’t the market simply provide them? Third, is the 401k savings case idiosyncratic or representative? The idea that the homo economicus, rational calculator, misses important features of human behavior, and would do with some insights from psychology, is not new, of course. Thaler’s prize is, at minimum, the fifth Nobel to go to someone pushing this general idea, since Herb Simon, Maurice Allais, Daniel Kahneman, and the aforementioned Bob Shiller have all already won. Copious empirical evidence, and indeed simple human observation, implies that people have behavioral biases, that they are not perfectly rational – as Thaler has noted, we see what looks like irrationality even in the composition of 100 million dollar baseball rosters. The more militant behavioralists insist that ignoring these psychological factors is unscientific! And yet, and yet: the vast majority of economists, all of whom are by now familiar with these illustrious laureates and their work, still use fairly standard expected utility maximizing agents in nearly all of our papers. Unpacking the three issues above will clarify how that could possibly be so.

Let’s discuss ethics first. Simply arguing that organizations “must” make a choice (as Thaler and Sunstein do) is insufficient; we would not say a firm that defaults consumers into an autorenewal for a product they rarely renew when making an active choice is acting “neutrally”. Nudges can be used for “good” or “evil”. Worse, whether a nudge is good or evil depends on the planner’s evaluation of the agent’s “inner rational self”, as Infante and Sugden, among others, have noted many times. That is, claiming paternalism is “only a nudge” does not excuse the paternalist from the usual moral philosophic critiques! Indeed, as Chetty and friends have argued, the more you believe behavioral biases exist and are “nudgeable”, the more careful you need to be as a policymaker about inadvertently reducing welfare. There is, I think, less controversy when we use nudges rather than coercion to reach some policy goal. For instance, if a policymaker wants to reduce energy usage, and is worried about distortionary taxation, nudges may (depending on how you think about social welfare with non-rational preferences!) be a better way to achieve the desired outcomes. But this goal is very different from the common justification that nudges somehow are pushing people toward policies they actually like in their heart of hearts. Carroll et al have a very nice theoretical paper trying to untangle exactly what “better” means for behavioral agents, and exactly when the imprecision of nudges or defaults given our imperfect knowledge of individual’s heterogeneous preferences makes attempts at libertarian paternalism worse than laissez faire.

What of the practical effects of nudges? How can they be so large, and in what contexts? Thaler has very convincingly shown that behavioral biases can affect real world behavior, and that understanding those biases means two policies which are identical from the perspective of a homo economicus model can have very different effects. But many economic situations involve players doing things repeatedly with feedback – where heuristics approximated by rationality evolve – or involve players who “perform poorly” being selected out of the game. For example, I can think of many simple nudges to get you or me to play better basketball. But when it comes to Michael Jordan, the first order effects are surely how well he takes cares of his health, the teammates he has around him, and so on. I can think of many heuristics useful for understanding how simple physics will operate, but I don’t think I can find many that would improve Einstein’s understanding of how the world works. The 401k situation is unusual because it is a decision with limited short-run feedback, taken by unsophisticated agents who will learn little even with experience. The natural alternative, of course, is to have agents outsource the difficult parts of the decision, to investment managers or the like. And these managers will make money by improving people’s earnings. No surprise that robo-advisors, index funds, and personal banking have all become more important as defined contribution plans have become more common! If we worry about behavioral biases, we ought worry especially about market imperfections that prevent the existence of designated agents who handle the difficult decisions for us.

The fact that agents can exist is one reason that irrationality in the lab may not translate into irrationality in the market. But even without agents, we might reasonably be suspect of some claims of widespread irrationality. Consider Thaler’s famous endowment effect: how much you are willing to pay for, say, a coffee mug or a pen is much less than how much you would accept to have the coffee mug taken away from you. Indeed, it is not unusual in a study to find a ratio of three times or greater between the willingness to pay and willingness to accept amount. But, of course, if these were “preferences”, you could be money pumped (see Yaari, applying a theorem of de Finetti, on the mathematics of the pump). Say you value the mug at ten bucks when you own it and five bucks when you don’t. Do we really think I can regularly get you to pay twice as much by loaning you the mug for free for a month? Do we see car companies letting you take a month-long test drive of a $20,000 car then letting you keep the car only if you pay $40,000, with some consumers accepting? Surely not. Now the reason why is partly what Laibson and Yariv argue, that money pumps do not exist in competitive economies since market pressure will compete away rents: someone else will offer you the car at $20,000 and you will just buy from them. But even if the car company is a monopolist, surely we find the magnitude of the money pump implied here to be on face ridiculous.

Even worse are the dictator games introduced in Thaler’s 1986 fairness paper. Students were asked, upon being given $20, whether they wanted to give an anonymous student half of their endowment or 10%. Many of the students gave half! This experiment has been repeated many, many times, with similar effects. Does this mean economists are naive to neglect the social preferences of humans? Of course not! People are endowed with money and gifts all the time. They essentially never give any of it to random strangers – I feel confident assuming you, the reader, have never been handed some bills on the sidewalk by an officeworker who just got a big bonus! Worse, the context of the experiment matters a ton (see John List on this point). Indeed, despite hundreds of lab experiments on dictator games, I feel far more confident predicting real world behavior following windfalls if we use a parsimonious homo economicus model than if we use the results of dictator games. Does this mean the games are useless? Of course not – studying what factors affect other-regarding preferences is interesting, and important. But how odd to have a branch of our field filled with people who see armchair theorizing of homo economicus as “unscientific”, yet take lab experiments so literally even when they are so clearly contrary to data?

To take one final example, consider Thaler’s famous model of “mental accounting”. In many experiments, he shows people have “budgets” set aside for various tasks. I have my “gas budget” and adjust my driving when gas prices change. I only sell stocks when I am up overall on that stock since I want my “mental account” of that particular transaction to be positive. But how important is this in the aggregate? Take the Engel curve. Budget shares devoted to food fall with income. This is widely established historically and in the cross section. Where is the mental account? Farber (2008 AER) even challenges the canonical account of taxi drivers working just enough hours to make their targeted income. As in the dictator game and the endowment effect, there is a gap between what is real, psychologically, and what is consequential enough to be first-order in our economic understanding of the world.

Let’s sum up. Thaler’s work is brilliant – it is a rare case of an economist taking psychology seriously and actually coming up with policy-relevant consequences like the 401k policy. But Thaler’s work is also dangerous to young economists who see biases everywhere. Experts in a field, and markets with agents and mechanisms and all the other tricks they develop, are very very good at ferreting out irrationality, and economists core skill lies in not missing those tricks.

Some remaining bagatelles: 1) Thaler and his PhD advisor, Sherwin Rosen, have one of the first papers on measuring the “statistical” value of a life, a technique now widely employed in health economics and policy. 2) Beyond his academic work, Thaler has won a modicum of fame as a popular writer (Nudge, written with Cass Sunstein, is canonical here) and for his brief turn as an actor alongside Selena Gomez in “The Big Short”. 3) Dick has a large literature on “fairness” in pricing, a topic which goes back to Thomas Aquinas, if not earlier. Many of the experiments Thaler performs, like the thought experiments of Aquinas, come down to the fact that many perceive market power to be unfair. Sure, I agree, but I’m not sure there’s much more that can be learned than this uncontroversial fact. 4) Law and econ has been massively influenced by Thaler. As a simple example, if endowment effects are real, then the assignment of property rights matters even when there are no transaction costs. Jolls et al 1998 go into more depth on this issue. 5) Thaler’s precise results in so-called behavioral finance are beyond my area of expertise, so I defer to John Cochrane’s comments following the 2013 Nobel. Eugene Fama is, I think, correct when he suggests that market efficiency generated by rational traders with risk aversion is the best model we have of financial behavior, where best is measured by “is this model useful for explaining the world.” The number of behavioral anomalies at the level of the market which persist and are relevant in the aggregate do not strike me as large, while the number of investors and policymakers who make dreadful decisions because they believe markets are driven by behavioral sentiments is large indeed!

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Nobel Prize 2016 Part II: Oliver Hart

The Nobel Prize in Economics was given yesterday to two wonderful theorists, Bengt Holmstrom and Oliver Hart. I wrote a day ago about Holmstrom’s contributions, many of which are simply foundational to modern mechanism design and its applications. Oliver Hart’s contribution is more subtle and hence more of a challenge to describe to a nonspecialist; I am sure of this because no concept gives my undergraduate students more headaches than Hart’s “residual control right” theory of the firm. Even stranger, much of Hart’s recent work repudiates the importance of his most famous articles, a point that appears to have been entirely lost on every newspaper discussion of Hart that I’ve seen (including otherwise very nice discussions like Applebaum’s in the New York Times). A major reason he has changed his beliefs, and his research agenda, so radically is not simply the whims of age or the pressures of politics, but rather the impact of a devastatingly clever, and devastatingly esoteric, argument made by the Nobel winners Eric Maskin and Jean Tirole. To see exactly what’s going on in Hart’s work, and why there remains many very important unsolved questions in this area, let’s quickly survey what economists mean by “theory of the firm”.

The fundamental strangeness of firms goes back to Coase. Markets are amazing. We have wonderful theorems going back to Hurwicz about how competitive market prices coordinate activity efficiently even when individuals only have very limited information about how various things can be produced by an economy. A pencil somehow involves graphite being mined, forests being explored and exploited, rubber being harvested and produced, the raw materials brought to a factory where a machine puts the pencil together, ships and trains bringing the pencil to retail stores, and yet this decentralized activity produces a pencil costing ten cents. This is the case even though not a single individual anywhere in the world knows how all of those processes up the supply chain operate! Yet, as Coase pointed out, a huge amount of economic activity (including the majority of international trade) is not coordinated via the market, but rather through top-down Communist-style bureaucracies called firms. Why on Earth do these persistent organizations exist at all? When should firms merge and when should they divest themselves of their parts? These questions make up the theory of the firm.

Coase’s early answer is that something called transaction costs exist, and that they are particularly high outside the firm. That is, market transactions are not free. Firm size is determined at the point where the problems of bureaucracy within the firm overwhelm the benefits of reducing transaction costs from regular transactions. There are two major problems here. First, who knows what a “transaction cost” or a “bureaucratic cost” is, and why they differ across organizational forms: the explanation borders on tautology. Second, as the wonderful paper by Alchian and Demsetz in 1972 points out, there is no reason we should assume firms have some special ability to direct or punish their workers. If your supplier does something you don’t like, you can keep them on, or fire them, or renegotiate. If your in-house department does something you don’t like, you can keep them on, or fire them, or renegotiate. The problem of providing suitable incentives – the contracting problem – does not simply disappear because some activity is brought within the boundary of the firm.

Oliver Williamson, a recent Nobel winner joint with Elinor Ostrom, has a more formal transaction cost theory: some relationships generate joint rents higher than could be generated if we split ways, unforeseen things occur that make us want to renegotiate our contract, and the cost of that renegotiation may be lower if workers or suppliers are internal to a firm. “Unforeseen things” may include anything which cannot be measured ex-post by a court or other mediator, since that is ultimately who would enforce any contract. It is not that everyday activities have different transaction costs, but that the negotiations which produce contracts themselves are easier to handle in a more persistent relationship. As in Coase, the question of why firms do not simply grow to an enormous size is largely dealt with by off-hand references to “bureaucratic costs” whose nature was largely informal. Though informal, the idea that something like transaction costs might matter seemed intuitive and had some empirical support – firms are larger in the developing world because weaker legal systems means more “unforeseen things” will occur outside the scope of a contract, hence the differential costs of holdup or renegotiation inside and outside the firm are first order when deciding on firm size. That said, the Alchian-Demsetz critique, and the question of what a “bureaucratic cost” is, are worrying. And as Eric van den Steen points out in a 2010 AER, can anyone who has tried to order paper through their procurement office versus just popping in to Staples really believe that the reason firms exist is to lessen the cost of intrafirm activities?

Grossman and Hart (1986) argue that the distinction that really makes a firm a firm is that it owns assets. They retain the idea that contracts may be incomplete – at some point, I will disagree with my suppliers, or my workers, or my branch manager, about what should be done, either because a state of the world has arrived not covered by our contract, or because it is in our first-best mutual interest to renegotiate that contract. They retain the idea that there are relationship-specific rents, so I care about maintaining this particular relationship. But rather than rely on transaction costs, they simply point out that the owner of the asset is in a much better bargaining position when this disagreement occurs. Therefore, the owner of the asset will get a bigger percentage of rents after renegotiation. Hence the person who owns an asset should be the one whose incentive to improve the value of the asset is most sensitive to that future split of rents.

Baker and Hubbard (2004) provide a nice empirical example: when on-board computers to monitor how long-haul trucks were driven began to diffuse, ownership of those trucks shifted from owner-operators to trucking firms. Before the computer, if the trucking firm owns the truck, it is hard to contract on how hard the truck will be driven or how poorly it will be treated by the driver. If the driver owns the truck, it is hard to contract on how much effort the trucking firm dispatcher will exert ensuring the truck isn’t sitting empty for days, or following a particularly efficient route. The computer solves the first problem, meaning that only the trucking firm is taking actions relevant to the joint relationship which are highly likely to be affected by whether they own the truck or not. In Grossman and Hart’s “residual control rights” theory, then, the introduction of the computer should mean the truck ought, post-computer, be owned by the trucking firm. If these residual control rights are unimportant – there is no relationship-specific rent and no incompleteness in contracting – then the ability to shop around for the best relationship is more valuable than the control rights asset ownership provides. Hart and Moore (1990) extends this basic model to the case where there are many assets and many firms, suggesting critically that sole ownership of assets which are highly complementary in production is optimal. Asset ownership affects outside options when the contract is incomplete by changing bargaining power, and splitting ownership of complementary assets gives multiple agents weak bargaining power and hence little incentive to invest in maintaining the quality of, or improving, the assets. Hart, Schleifer and Vishny (1997) provide a great example of residual control rights applied to the question of why governments should run prisons but not garbage collection. (A brief aside: note the role that bargaining power plays in all of Hart’s theories. We do not have a “perfect” – in a sense that can be made formal – model of bargaining, and Hart tends to use bargaining solutions from cooperative game theory like the Shapley value. After Shapley’s prize alongside Roth a few years ago, this makes multiple prizes heavily influenced by cooperative games applied to unexpected problems. Perhaps the theory of cooperative games ought still be taught with vigor in PhD programs!)

There are, of course, many other theories of the firm. The idea that firms in some industries are big because there are large fixed costs to enter at the minimum efficient scale goes back to Marshall. The agency theory of the firm going back at least to Jensen and Meckling focuses on the problem of providing incentives for workers within a firm to actually profit maximize; as I noted yesterday, Holmstrom and Milgrom’s multitasking is a great example of this, with tasks being split across firms so as to allow some types of workers to be given high powered incentives and others flat salaries. More recent work by Bob Gibbons, Rebecca Henderson, Jon Levin and others on relational contracting discusses how the nexus of self-enforcing beliefs about how hard work today translates into rewards tomorrow can substitute for formal contracts, and how the credibility of these “relational contracts” can vary across firms and depend on their history.

Here’s the kicker, though. A striking blow was dealt to all theories which rely on the incompleteness or nonverifiability of contracts by a brilliant paper of Maskin and Tirole (1999) in the Review of Economic Studies. Theories relying on incomplete contracts generally just hand-waved that there are always events which are unforeseeable ex-ante or impossible to verify in court ex-post, and hence there will always scope for disagreement about what to do when those events occur. But, as Maskin and Tirole correctly point out, agent don’t care about anything in these unforeseeable/unverifiable states except for what the states imply about our mutual valuations from carrying on with a relationship. Therefore, every “incomplete contract” should just involve the parties deciding in advance that if a state of the world arrives where you value keeping our relationship in that state at 12 and I value it at 10, then we should split that joint value of 22 at whatever level induces optimal actions today. Do this same ex-ante contracting for all future profit levels, and we are done. Of course, there is still the problem of ensuring incentive compatibility – why would the agents tell the truth about their valuations when that unforeseen event occurs? I will omit the details here, but you should read the original paper where Maskin and Tirole show a (somewhat convoluted but still working) mechanism that induces truthful revelation of private value by each agent. Taking the model’s insight seriously but the exact mechanism less seriously, the paper basically suggests that incomplete contracts don’t matter if we can truthfully figure out ex-post who values our relationship at what amount, and there are many real-world institutions like mediators who do precisely that. If, as Maskin and Tirole prove (and Maskin described more simply in a short note), incomplete contracts aren’t a real problem, we are back to square one – why have persistent organizations called firms?

What should we do? Some theorists have tried to fight off Maskin and Tirole by suggesting that their precise mechanism is not terribly robust to, for instance, assumptions about higher-order beliefs (e.g., Aghion et al (2012) in the QJE). But these quibbles do not contradict the far more basic insight of Maskin and Tirole, that situations we think of empirically as “hard to describe” or “unlikely to occur or be foreseen”, are not sufficient to justify the relevance of incomplete contracts unless we also have some reason to think that all mechanisms which split rent on the basis of future profit, like a mediator, are unavailable. Note that real world contracts regularly include provisions that ex-ante describe how contractual disagreement ex-post should be handled.

Hart’s response, and this is both clear from his CV and from his recent papers and presentations, is to ditch incompleteness as the fundamental reason firms exist. Hart and Moore’s 2007 AER P&P and 2006 QJE are very clear:

Although the incomplete contracts literature has generated some useful insights about firm boundaries, it has some shortcomings. Three that seem particularly important to us are the following. First, the emphasis on noncontractible ex ante investments seems overplayed: although such investments are surely important, it is hard to believe that they are the sole drivers of organizational form. Second, and related, the approach is ill suited to studying the internal organization of firms, a topic of great interest and importance. The reason is that the Coasian renegotiation perspective suggests that the relevant parties will sit down together ex post and bargain to an efficient outcome using side payments: given this, it is hard to see why authority, hierarchy, delegation, or indeed anything apart from asset ownership matters. Finally, the approach has some foundational weaknesses [pointed out by Maskin and Tirole (1999)].

To my knowledge, Oliver Hart has written zero papers since Maskin-Tirole was published which attempt to explain any policy or empirical fact on the basis of residual control rights and their necessary incomplete contracts. Instead, he has been primarily working on theories which depend on reference points, a behavioral idea that when disagreements occur between parties, the ex-ante contracts are useful because they suggest “fair” divisions of rent, and induce shading and other destructive actions when those divisions are not given. These behavioral agents may very well disagree about what the ex-ante contract means for “fairness” ex-post. The primary result is that flexible contracts (e.g., contracts which deliberately leave lots of incompleteness) can adjust easily to changes in the world but will induce spiteful shading by at least one agent, while rigid contracts do not permit this shading but do cause parties to pursue suboptimal actions in some states of the world. This perspective has been applied by Hart to many questions over the past decade, such as why it can be credible to delegate decision making authority to agents; if you try to seize it back, the agent will feel aggrieved and will shade effort. These responses are hard, or perhaps impossible, to justify when agents are perfectly rational, and of course the Maskin-Tirole critique would apply if agents were purely rational.

So where does all this leave us concerning the initial problem of why firms exist in a sea of decentralized markets? In my view, we have many clever ideas, but still do not have the perfect theory. A perfect theory of the firm would need to be able to explain why firms are the size they are, why they own what they do, why they are organized as they are, why they persist over time, and why interfirm incentives look the way they do. It almost certainly would need its mechanisms to work if we assumed all agents were highly, or perfectly, rational. Since patterns of asset ownership are fundamental, it needs to go well beyond the type of hand-waving that makes up many “resource” type theories. (Firms exist because they create a corporate culture! Firms exist because some firms just are better at doing X and can’t be replicated! These are outcomes, not explanations.) I believe that there are reasons why the costs of maintaining relationships – transaction costs – endogenously differ within and outside firms, and that Hart is correct is focusing our attention on how asset ownership and decision making authority affects incentives to invest, but these theories even in their most endogenous form cannot do everything we wanted a theory of the firm to accomplish. I think that somehow reputation – and hence relational contracts – must play a fundamental role, and that the nexus of conflicting incentives among agents within an organization, as described by Holmstrom, must as well. But we still lack the precise insight to clear up this muddle, and give us a straightforward explanation for why we seem to need “little Communist bureaucracies” to assist our otherwise decentralized and almost magical market system.

Reinhard Selten and the making of modern game theory

Reinhard Selten, it is no exaggeration, is a founding father of two massive branches of modern economics: experiments and industrial organization. He passed away last week after a long and idiosyncratic life. Game theory as developed by the three co-Nobel laureates Selten, Nash, and Harsanyi is so embedded in economic reasoning today that, to a great extent, it has replaced price theory as the core organizing principle of our field. That this would happen was not always so clear, however.

Take a look at some canonical papers before 1980. Arrow’s Possibility Theorem simply assumed true preferences can be elicited; not until Gibbard and Satterthwaite do we answer the question of whether there is even a social choice rule that can elicit those preferences truthfully! Rothschild and Stiglitz’s celebrated 1976 essay on imperfect information in insurance markets defines equilibria in terms of a individual rationality, best responses in the Cournot sense, and free entry. How odd this seems today – surely the natural equilibrium in an insurance market depends on beliefs about the knowledge held by others, and beliefs about those beliefs! Analyses of bargaining before Rubinstein’s 1982 breakthrough nearly always rely on axioms of psychology rather than strategic reasoning. Discussions of predatory pricing until the 1970s, at the very earliest, relied on arguments that we now find unacceptably loose in their treatment of beliefs.

What happened? Why didn’t modern game-theoretic treatment of strategic situations – principally those involve more than one agent but less than an infinite number, although even situations of perfect competition now often are motivated game theoretically – arrive soon after the proofs of von Neumann, Morganstern, and Nash? Why wasn’t the Nash program, of finding justification in self-interested noncooperative reasoning for cooperative or axiom-driven behavior, immediately taken up? The problem was that the core concept of the Nash equilibrium simply permits too great a multiplicity of outcomes, some of which feel natural and others of which are less so. As such, a long search, driven essentially by a small community of mathematicians and economists, attempted to find the “right” refinements of Nash. And a small community it was: I recall Drew Fudenberg telling a story about a harrowing bus ride at an early game theory conference, where a fellow rider mentioned offhand that should they crash, the vast majority of game theorists in the world would be wiped out in one go!

Selten’s most renowned contribution came in the idea of perfection. The concept of subgame perfection was first proposed in a German-language journal in 1965 (making it one of the rare modern economic classics inaccessible to English speakers in the original, alongside Maurice Allais’ 1953 French-language paper in Econometrica which introduces the Allais paradox). Selten’s background up to 1965 is quite unusual. A young man during World War II, raised Protestant but with one Jewish parent, Selten fled Germany to work on farms, and only finished high school at 20 and college at 26. His two interests were mathematics, for which he worked on the then-unusual extensive form game for his doctoral degree, and experimentation, inspired by the small team of young professors at Frankfurt trying to pin down behavior in oligopoly through small lab studies.

In the 1965 paper, on demand inertia (paper is gated), Selten wrote a small game theoretic model to accompany the experiment, but realized there were many equilibria. The term “subgame perfect” was not introduced until 1974, also by Selten, but the idea itself is clear in the ’65 paper. He proposed that attention should focus on equilibria where, after every action, each player continues to act rationally from that point forward; that is, he proposed that in every “subgame”, or every game that could conceivably occur after some actions have been taken, equilibrium actions must remain an equilibrium. Consider predatory pricing: a firm considers lowering price below cost today to deter entry. It is a Nash equilibrium for entrants to believe the price would continue to stay low should they enter, and hence to not enter. But it is not subgame perfect: the entrant should reason that after entering, it is not worthwhile for the incumbent to continue to lose money once the entry has already occurred.

Complicated strings of deductions which rule out some actions based on faraway subgames can seem paradoxical, of course, and did even to Selten. In his famous Chain Store paradox, he considers a firm with stores in many locations choosing whether to price aggressively to deter entry, with one potential entrant in each town choosing one at a time whether to enter. Entrants prefer to enter if pricing is not aggressive, but prefer to remain out otherwise; incumbents prefer to price nonaggressively either if entry occurs or not. Reasoning backward, in the final town we have the simple one-shot predatory pricing case analyzed above, where we saw that entry is the only subgame perfect equilibria. Therefore, the entrant in the second-to-last town knows that the incumbent will not fight entry aggressively in the final town, hence there is no benefit to doing so in the second-to-last town, hence entry occurs again. Reasoning similarly, entry occurs everywhere. But if the incumbent could commit in advance to pricing aggressively in, say, the first 10 towns, it would deter entry in those towns and hence its profits would improve. Such commitment may not possible, but what if the incumbent’s reasoning ability is limited, and it doesn’t completely understand why aggressive pricing in early stages won’t deter the entrant in the 16th town? And what if entrants reason that the incumbent’s reasoning ability is not perfectly rational? Then aggressive pricing to deter entry can occur.

That behavior may not be perfectly rational but rather bounded had been an idea of Selten’s since he read Herbert Simon as a young professor, but in his Nobel Prize biography, he argues that progress on a suitable general theory of bounded rationality has been hard to come by. The closest Selten comes to formalizing the idea is in his paper on trembling hand perfection in 1974, inspired by conversations with John Harsanyi. The problem with subgame perfection had been noted: if an opponent takes an action off the equilibrium path, it is “irrational”, so why should rationality of the opponent be assumed in the subgame that follows? Harsanyi assumes that tiny mistakes can happen, putting even rational players into subgames. Taking the limit as mistakes become infinitesimally rare produces the idea of trembling-hand perfection. The idea of trembles implicitly introduces the idea that players have beliefs at various information sets about what has happened in the game. Kreps and Wilson’s sequential equilibrium recasts trembles as beliefs under uncertainty, and showed that a slight modification of the trembling hand leads to an easier decision-theoretic interpretation of trembles, an easier computation of equilibria, and an outcome that is nearly identical to Selten’s original idea. Sequential equilibria, of course, goes on to become to workhorse solution concept in dynamic economics, a concept which underscores essentially all of modern industrial organization.

That Harsanyi, inventor of the Bayesian game, is credited by Selten for inspiring the trembling hand paper is no surprise. The two had met at a conference in Jerusalem in the mid-1960s, and they’d worked together both on applied projects for the US military, and on pure theory research while Selten visiting Berkeley. A classic 1972 paper of theirs on Nash bargaining with incomplete information (article is gated) begins the field of cooperative games with incomplete information. And this was no minor field: Roger Myerson, in his paper introducing mechanism design under incomplete information – the famous Bayesian revelation principle paper – shows that there exists a unique Selten-Harsanyi bargaining solution under incomplete information which is incentive compatible.

Myerson’s example is amazing. Consider building a bridge which costs $100. Two people will use the bridge. One values the bridge at $90. The other values the bridge at $90 with probability .9, and $30 with probability p=.1, where that valuation is the private knowledge of the second person. Note that in either case, the bridge is worth building. But who should pay? If you propose a 50/50 split, the bridge will simply not be built 10% of the time. If you propose an 80/20 split, where even in their worst case situation each person gets a surplus value of ten dollars, the outcome is unfair to player one 90% of the time (where “unfair” will mean, violates certain principles of fairness that Nash, and later Selten and Harsanyi, set out axiomatically). What of the 53/47 split that gives each party, on average, the same split? Again, this is not “interim incentive compatible”, in that player two will refuse to pay in the case he is the type that values the bridge only at $30. Myerson shows mathematically that both players will agree once they know their private valuations to the following deal, and that the deal satisfies the Selten-Nash fairness axioms: when player 2 claims to value at $90, the payment split is 49.5/50.5 and the bridge is always built, but when player 2 claims to value at $30, the entire cost is paid by player 1 but the bridge is built with only probability .439. Under this split, there are correct incentives for player 2 to always reveal his true willingness to pay. The mechanism means that there is a 5.61 percent chance the bridge isn’t built, but the split of surplus from the bridge nonetheless does better than any other split which satisfies all of Harsanyi and Selten’s fairness axioms.

Selten’s later work is, it appears to me, more scattered. His attempt with Harsanyi to formalize “the” equilibrium refinement, in a 1988 book, was a valiant but in the end misguided attempt. His papers on theoretical biology, inspired by his interest in long walks among the wildflowers, are rather tangential to his economics. And what of his experimental work? To understand Selten’s thinking, read this fascinating dialogue with himself that Selten gave as a Schwartz Lecture at Northwestern MEDS. In this dialogue, he imagines a debate between a Bayesian economist, experimentalist, and an evolutionary biologist. The economist argues that “theory without theorems” is doomed to fail, that Bayesianism is normatively “correct”, and the Bayesian reasoning can easily be extended to include costs of reasoning or reasoning mistakes. The experimentalist argues that ad hoc assumptions are better than incorrect ones: just as human anatomy is complex and cannot be reduced to a few axioms, neither can social behavior. The biologist argues that learning a la Nelson and Winter is descriptively accurate as far as how humans behave, whereas high level reasoning is not. The “chairman”, perhaps representing Selten himself, sums up the argument as saying that experiments which simply contradict Bayesianism are a waste of time, but that human social behavior surely depends on bounded rationality and hence empirical work ought be devoted to constructing a foundation for such a theory (shall we call this the “Selten program”?). And yet, this essay was from 1990, and we seem no closer to having such a theory, nor does it seem to me that behavioral research has fundamentally contradicted most of our core empirical understanding derived from theories with pure rationality. Selten’s program, it seems, remains not only incomplete, but perhaps not even first order; the same cannot be said of his theoretical constructs, as without perfection a great part of modern economics simply could not exist.

Nobel Prize 2014: Jean Tirole

A Nobel Prize for applied theory – now this something I can get behind! Jean Tirole’s prize announcement credits him for his work on market power and regulation, and there is no question that he is among the leaders, if not the world leader, in the application of mechanism design theory to industrial organization; indeed, the idea of doing IO in the absence of this theoretical toolbox seems so strange to me that it’s hard to imagine anyone had ever done it! Economics is sometimes defined by a core principle that agents – people or firms – respond to incentives. Incentives are endogenous; how my bank or my payment processor or my lawyer wants to act depends on how other banks or other processors or other prosecutors act. Regulation is therefore a game. Optimal regulation is therefore a problem of mechanism design, and we now have mathematical tools that allow investigation across the entire space of potential regulating mechanisms, even those that our counterfactual. That is an incredibly powerful methodological advance, so powerful that there will be at least one more Nobel (Milgrom and Holmstrom?) based on this literature.

Because Tirole’s toolbox is theoretical, he has written an enormous amount of “high theory” on the implications of the types of models modern IO economists use. I want to focus in this post on a particular problem where Tirole has stood on both sides of the divide: that of the seemingly obscure question of what can be contracted on.

This literature goes back to a very simple question: what is a firm, and why do they exist? And when they exist, why don’t they grow so large that they become one giant firm a la Schumpeter’s belief in Capitalism, Socialism, and Democracy? One answer is that given by Coase and updated by Williamson, among many others: transaction costs. There are some costs of haggling or similar involved in getting things done with suppliers or independent contractors. When these costs are high, we integrate that factor into the firm. When they are low, we avoid the bureaucratic costs needed to manage all those factors.

For a theorist trained in mechanism design, this is a really strange idea. For one, what exactly are these haggling or transaction costs? Without specifying what precisely is meant, it is very tough to write a model incorporating them and exploring the implications of them. But worse, why would we think these costs are higher outside the firm than inside? A series of papers by Sandy Grossman, Oliver Hart and John Moore point out, quite rightly, that firms cannot make their employees do anything. They can tell them to do something, but the employees will respond to incentives like anyone else. Given that, why would we think the problem of incentivizing employees within an organization is any easier or harder than incentivizing them outside the organization? The solution they propose is the famous Property Rights Theory of the firm (which could fairly be considered the most important paper ever published in the illustrious JPE). This theory says that firms are defined by the assets they control. If we can contract on every future state of the world, then this control shouldn’t matter, but when unforeseen contingencies arise, the firm still has “residual control” of its capital. Therefore, efficiency depends on the allocation of scarce residual control rights, and hence the allocation of these rights inside or outside of a firm are important. Now that is a theory of the firm – one well-specified and based on incentives – that I can understand. (An interesting sidenote: when people think economists don’t really understand the economy because, hey, they’re not rich, we can at least point to Sandy Grossman. Sandy, a very good theorist, left academia to start his own firm, and as far as I know, he is now a billionaire!)

Now you may notice one problem with Grossman, Hart and Moore’s papers. As there was an assumption of nebulous transaction costs in Coase and his followers, there is a nebulous assumption of “incomplete contracts” in GHM. This seems reasonable at first glance: there is no way we could possibly write a contract that covers every possible contingency or future state of the world. I have to imagine everyone that has ever rented an apartment or leased a car or ran a small business has first-hand experience with the nature of residual control rights when some contingency arises. Here is where Tirole comes in. Throughout the 80s and 90s, Tirole wrote many papers using incomplete contracts: his 1994 paper with Aghion on contracts for R&D is right within this literature. In complete contracting, the courts can verify and enforce any contract that relies on observable information, though adverse selection (hidden information by agents) or moral hazard (unverifiable action by agents) may still exist. Incomplete contracting further restricts the set of contracts to a generally simple set of possibilities. In the late 1990s, however, Tirole, along with his fellow Nobel winner Eric Maskin, realized in an absolute blockbuster of a paper that there is a serious problem with these incomplete contracts as usually modeled.

Here is why: even if we can’t ex-ante describe all the future states of the world, we may still ex-post be able to elicit information about the payoffs we each get. As Tirole has noted, firms do not care about indescribable contingencies per se; they only care about how those contingencies affect their payoffs. That means that, at an absolute minimum, the optimal “incomplete contract” better be at least as good as the optimal contract which conditions on elicited payoffs. These payoffs may be stochastic realizations of all of our actions, of course, and hence this insight might not actually mean we can first-best efficiency when the future is really hard to describe. Maskin and Tirole’s 1999 paper shows, incredibly, that indescribability of states is irrelevant, and that even if we can’t write down a contract on states of the world, we can contract on payoff realizations in a way that is just as good as if we could actually write the complete contract.

How could this be? Imagine (here via a simple example of Maskin’s) two firms contracting for R&D. Firm 1 exerts effort e1 and produces a good with value v(e1). Firm 2 invests in some process that will lower the production cost of firm 1’s new good, investing e2 to make production cost equal to c(e2). Payoffs, then, are u1(p-c(e2)-e1) and u2(v(e1)-p-e2). If we knew u1 and u2 and could contract upon it, then the usual Nash implementation literature tells us how to generate efficient levels of e1 and e2 (call them e1*, e2*) by writing a contract: if the product doesn’t have the characteristics of v(e1*) and the production process doesn’t have the characteristics of c(e2*), then we fine the person who cheated. If effort generated stochastic values rather than absolute ones, the standard mechanism design literature tells us exactly when we can still get the first best.

Now, what if v and c are state-dependent, and there are huge number of states of the world? That is, efficient e1* and e2* are now functions of the state of the world realized after we write the initial contract. Incomplete contracting assumed that we cannot foresee all the possible v and c, and hence won’t write a contract incorporating all of them. But, aha!, we can still write a contract that says, look, whatever happens tomorrow, we are going to play a game tomorrow where I say what my v is and you say what your c is. It turns out that there exists such a game which generates truthful revelation of v and c (Maskin and Tirole do this using an idea similar to that of the subgame implementation literature, but the exact features are not terribly important for our purposes). Since the only part of the indescribable state I care about is the part that affects my payoffs, we are essentially done: no matter how many v and c’s there could be in the future, as long as I can write a contract specifying how we each get other to truthfully say what those parameters are, this indescribability doesn’t matter.

Whoa. That is a very, very, very clever insight. Frankly, it is convincing enough that the only role left for property rights theories of the firm are some kind of behavioral theory which restricts even contracts of the Maskin-Tirole sense – and since these contracts are quite a bit simpler in some way than the hundreds of pages of legalese which we see in a lot of real-world contracts on important issues, it’s not clear that bounded rationality or similar theories will get us far.

Where to go from here? Firms, and organizations more generally, exist. I am sure the reason has to do with incentives. But exactly why – well, we still have a lot of work to do in explaining why. And Tirole has played a major role in explaining why.

Tirole’s Walras-Bowley lecture, published in Econometrica in 1999, is a fairly accessible introduction to his current view of incomplete contracts. He has many other fantastic papers, across a wide variety of topics. I particularly like his behavioral theory written mainly with Roland Benabou; see, for instance, their 2003 ReStud on when monetary rewards are bad for incentives.

“Seeking the Roots of Entrepreneurship: Insights from Behavioral Economics,” T. Astebro, H. Herz, R. Nanda & R. Weber (2014)

Entrepreneurship is a strange thing. Entrepreneurs work longer hours, make less money in expectation, and have higher variance earnings than those working for firms; if anyone knows of solid evidence to the contrary, I would love to see the reference. The social value of entrepreneurship through greater product market competition, new goods, etc., is very high, so as a society the strange choice of entrepreneurs may be a net benefit. We even encourage it here at UT! Given these facts, why does anyone start a company anyway?

Astebro and coauthors, as part of a new JEP symposium on entrepreneurship, look at evidence from behavioral economics. The evidence isn’t totally conclusive, but it appears entrepreneurs are not any more risk-loving or ambiguity-loving than the average person. Though they are overoptimistic, you still see entrepreneurs in high-risk, low-performance firms even ten years after they are founded, at which point surely any overoptimism must have long since been beaten out of them.

It is, however, true that entrepreneurship is much more common among the well-off. If risk aversion can’t explain things, then perhaps entrepreneurship is in some sense consumption: the founders value independence and control. Experimental evidence provides fairly strong evidence for this hypothesis. For many entrepreneurs, it is more about not having a boss than about the small chance of becoming very rich.

This leads to a couple questions: why so many immigrant entrepreneurs, and what are we make of the declining rate of firm formation in the US? Pardon me if I speculate a bit here. The immigrant story may just be selection; almost by definition, those who move across borders, especially those who move for graduate school, tend to be quite independent! The declining rate of firm formation may be tied with inequality changes; to the extent that entrepreneurship involves consumption of a luxury good (control over one’s working life) in addition to standard risk-adjusted cost-benefit analysis, then changes in the income distribution will change that consumption pattern. More work is needed on these questions.

Summer 2014 JEP (RePEc IDEAS). As always, a big thumbs up to the JEP for being free to read! It is also worth checking out the companion articles by Bill Kerr and coauthors on experimentation, with some amazing stats using internal VC project evaluation data for which ex-ante projections were basically identical for ex-post failures and ex-post huge successes, and one by Haltiwanger and coauthors documenting the important role played by startups in job creation, the collapse in startup formation and job churn which began well before 2008, and the utter mystery about what is causing this collapse (which we can see across regions and across industries).

“Incentives for Unaware Agents,” E.L. von Thadden & X. Zhao (2012)

There is a paradox that troubles a lot of applications of mechanism design: complete contracts (or, indeed, conditional contracts of any kind!) appear to be quite rare in the real world. One reason for this may be that agents are simply unaware of what they can do, an idea explored by von Thadden and Zhao in this article as well as by Rubinstein and Glazer in a separate 2012 paper in the JPE. I like the opening example in Rubinstein and Glazer:

“I went to a bar and was told it was full. I asked the bar hostess by what time one should arrive in order to get in. She said by 12 PM and that once the bar is full you can only get in if you are meeting a friend who is already inside. So I lied and said that my friend was already inside. Without having been told, I would not have known which of the possible lies to tell in order to get in.”

The contract itself gave the agent the necessary information. If I don’t specify the rule that patrons whose friend is inside are allowed entry, then only those who are aware of that possibility will ask. Of course, some patrons who I do wish to allow in, because their friend actually is inside, won’t know to ask unless I tell them. If the harm to the bar from previously unaware people learning and then lying overwhelms the gain from allowing unaware friends in, then the bar is better off not giving an explicit “contract”. Similar problems occur all the time. There are lots of behavioral explanations (recall the famous Israeli daycare which was said to have primed people into an “economic relationship” state of mind by setting a fine for picking kids up late, leading to more lateness, not less). But the bar story above relies on no behavioral action aside from agents having a default (ask about the friend clause if aware, or don’t ask if unaware) which can be removed if agents are informed about their real possible actions when given a contract.

When all agents are unaware, the tradeoff is simple, as above: I make everyone aware of their true actions if the cost of providing incentive rents is exceeded by the benefit of agents switching to actions I prefer more. Imagine that agents can not clean, partially clean, or fully clean their tools at the end of the workday (giving some stochastic output of cleanliness). They get no direct utility out of cleaning, and indeed get disutility the more time they spend cleaning. If there is no contract, they default to partially cleaning. If there is a contract, then if all cleaning pays the same the agent will exert zero effort and not clean. The only reason I might offer high-powered incentives, then, is if the benefit of getting agents to fully clean their tools exceeds the IC rents I will have to pay them once the contract is in place.

More interesting is the case with aware and unaware agents, when I don’t know which agent is which. The unaware agents gets contracts that pay the same wage no matter what their output, and the aware agents can get high-powered incentives. Solving the contracting problem involves a number of technical difficulties (standard envelope theorem arguments won’t work), but the solution is fairly intuitive. Offer two incomplete wage contracts w(x) and v(x). Let v(x) just fully insure: no matter what the output, the wage is the same. Let w(x) increase with better outputs. Choose the full insurance wage v low enough that the unaware agents’ participation constraint just binds. Then offer just enough rents in w(x) that the aware agents, who can take any action they want, actually take the planner preferred action. Unlike in a standard screening problem, I can manipulate this problem by just telling unaware agents about their possible actions: it turns out that profits only increase by making these agents aware if there are sufficiently few unaware agents in the population.

Some interesting sidenotes. Unawareness is “stable” in the sense that unaware agents will never be told they are unaware, and hence if we played this game for two periods, they would remain unaware. It is not optimal for aware agents to make unaware agents aware, since the aware earn information rents as a result of that unawareness. It is not optimal for the planner to make unaware agents aware: the firm is maximizing total profit, announcements strictly decrease wages of aware agents (by taking their information rents), and don’t change unaware agents rents (they get zero since their wage is always chosen to make their PC bind, as is usual for “low types” in screening problems). Interesting.

2009 working paper (IDEAS). Final version in REStud 2012. The Rubinstein/Glazer paper takes a slightly different tack. Roughly, it says that contract designers can write a codex of rules, where you are accepted if you satisfy all the rules. An agent made aware of the rules can figure out how to lie if it involves only lying about one rule. A patient, for instance, may want a painkiller prescription. He can lie about any (unverifiable) condition, but he is only smart enough to lie once. The question is, which codices are not manipulable?

“Until the Bitter End: On Prospect Theory in a Dynamic Context,” S. Ebert & P. Strack (2012)

Let’s kick off job market season with an interesting paper by Sebastian Ebert, a post-doc at Bonn, and Philipp Strack, who is on the job market from Bonn (though this doesn’t appear to be his main job market paper). The paper concerns the implications of Tversky and Kahneman’s prospect theory is its 1992 form. This form of utility is nothing obscure: the 1992 paper has over 5,000 citations, and the original prospect theory paper has substantially more. Roughly, cumulative prospect theory (CPT) says that agents have utility which is concave above a reference point, convex below it, with big losses and gains that occur with small probability weighed particularly heavily. Such loss aversion is thought to explain, for example, the simultaneous existence of insurance and gambling, or the difference in willingness to pay for objects you possess versus objects you don’t possess.

As Machina, among others, pointed out a couple decades ago, once you leave expected utility, you are definitely going to be writing down preferences that generate strange behavior at least somewhere. This is a direct result of Savage’s theorem. If you are not an EU-maximizer, then you are violating at least one of Savage’s axioms, and those axioms in their totality are proven to avoid many types of behavior that we find normatively unappealing such as falling for the sunk cost fallacy. Ebert and Strack write down a really general version of CPT, even more general than the rough definition I gave above. They then note that loss aversion means I can always construct a right-skewed gamble with negative expected payout that the loss averse agent will accept. Why? Agents like big gains that occur with small probability. Right-skew the gamble so that a big gain occurs with a tiny amount of probability, and otherwise the agent loses a tiny amount. An agent with CPT preferences will accept this gamble. Such a gamble exists at any wealth level, no matter what the reference point. Likewise, there is a left-skewed, positive expected payoff gamble that is rejected at any wealth level.

If you take a theory-free definition of risk aversion to mean “Risk-averse agents never accept gambles with zero expected payoff” and “Risk-loving agents always accept a risk with zero expected payoff”, then the theorem in the previous paragraph means that CPT agents are neither risk-averse, nor risk-loving, at any wealth level. This is interesting because a naive description of the loss averse utility function is that CPT agents are “risk-averse above the reference point, and risk-loving below it”. But the fact that small probability events are given more weight, in Ebert and Strack’s words, dominates whatever curvature the utility function possesses when it comes to some types of gambles.

So what does this mean, then? Let’s take CPT agents into a dynamic framework, and let them be naive about their time inconsistency (since they are non EU-maximizers, they will be time inconsistent). Bring them to a casino where a random variable moves with negative drift. Give them an endowment of money and any reference point. The CPT agent gambles at any time t as long as she has some strategy which (naively) increases her CPT utility. By the skewness result above, we know she can, at the very least, gamble a very small amount, plan to stop if I lose, and plan to keep gambling if I win. There is always such a bet. If I do lose, then tomorrow I will bet again, since there is a gamble with positive expected utility gain no matter my wealth level. Since the process has negative drift, I will continue gambling until I go bankrupt. This result isn’t relying on any strange properties of continuous time or infinite state spaces; the authors construct an example on a 37-number roulette wheel using the original parameterization of Kahneman and Tversky which has the CPT agent bet all the way to bankruptcy.

What do we learn? Two things. First, a lot of what is supposedly explained by prospect theory may, in fact, be explained by the skewness preference which the heavy weighting on low probability events in CPT, a fact mentioned by a number of papers the authors cite. Second, not to go all Burke on you, but when dealing with qualitative models, we have good reason to stick to the orthodoxy in many cases. The logical consequences of orthodox models will generally have been explored in great depth. The logical consequences of alternatives will not have been explored in the same way. All of our models of dynamic utility are problematic: expected utility falls in the Rabin critique, ambiguity aversion implies sunk cost fallacies, and prospect theory is vulnerable in the ways described here. But any theory which has been used for a long time will have its flaws shown more visibly than newer, alternative theories. We shouldn’t mistake the lack of visible flaws for their lack more generally.

SSRN Feb. 2012 working paper (no IDEAS version).