You are currently browsing the monthly archive for August 2014.

200 students for a 9 am class in spite of a midterm on day 3; perhaps they’ve not read the syllabus.

Began with the ultimatum game framed in terms of a seller making a take or leave it offer to the buyer. The game allows one to make two points at the very beginning of class.

1) The price seller chooses depends on their model of how the buyer will behave. One can draw this point out by asking sellers to explain how they came by their offers. Best offers to discuss are the really low ones (i.e. give most of the surplus to the buyer) and the offers that split the difference.

2) Under the assumption that `more money is better than less’, point out that the seller captures most of the gains from trade. Why? The ability to make a credible take or leave it offer.

This makes for a smooth transition into the model of quasi-linear preferences. Some toy examples of how buyers make choices based on surplus. Emphasize it captures idea that buyers make trade-offs (pay more if you get more; if its priced low enough its good enough). Someone will ask about budget constraints. A good question, ignore budget for now and come back to it later in the semester.

Next, point out that buyers do not share the same reservation price (RP) for a good or service. Introduce demand curve as vehicle for summarizing variation in RPs. Emphasize that demand curve tells you demand as you change your price holding other prices fixed.

Onto monopoly with constant unit costs and limited to a uniform price. Emphasize that monopoly in our context does not mean absence of competition, only that competition keeps price fixed as we change ours. Reason for such an assumption is to understand first how buyers respond to one sellers price changes.

How does monopoly choose profit maximizing price? Trade-off between margin and volume. Simple monopoly pricing exercise. Answer by itself is uninteresting. Want to know what profit maximizing depends upon.

Introduce elasticity of demand, its meaning and derivation. Then, a table of how profit and elasticity vary with price in the toy example introduce earlier. Point out how elasticity rises as price rises. Demand starts to drop off faster than margin rises. Explain why we don’t stop where elasticity is 1. Useful place to point out that here a small price increase is revenue neutral but total costs fall. So, uniform price is doing things: determining how much is captured from buyers and controlling total production costs. Table also illustrates that elasticity of demand matters for choosing price.

Segue into the markup formula. Explain why we should expect some kind of inverse relationship between markup and elasticity. Do derivation of markup formula with constant unit costs.

Now to something interesting to make the point that what has come before is very useful: author vs. publisher, who would prefer a higher price for the book? You’ll get all possible answers which is perfect. Start with how revenue is different from profit (authors get percentage revenue). This difference means their interests are not aligned. So, they should pick different prices. But which will be larger? Enter markup formula. Author wants price where elasticity is 1. Publisher wants to price where elasticity is bigger than 1. So, publisher wants higher price. Wait, what about e-books? Then, author and publisher want same price because unit costs are zero.

This is the perfect opportunity to introduce the Amazon letter to authors telling them that elasticity of demand for e-books at the current $14.99 price is about 2.4. Well above 1. Clearly, all parties should agree to lower the price of e-books. But what about traditional books? Surely lower e-book price will cause some readers to switch from the traditional to the e-book. Shouldn’t we look at the loss in profit from that as well? Capital point, but make life simple. Suppose we have only e-books. Notice, under the agency model where Amazon gets a percentage of revenue, everyone’s incentives appear to be aligned.

Is Amazon correct in its argument that dropping the e-book price will benefit me the author? As expressed in their letter, no. To say that the elasticity of demand for my book at the current price is 2.4 means that if I drop my price 1%, demand will rise 2.4% HOLDING OTHER PRICES FIXED. However, Amazon is not taking about dropping the price of my book alone. They are urging a drop in the price of ALL books. It may well be that a drop in price for all e-books will result in an increase in total revenues for the e-book category. This is good for Amazon. However, it is not at all clear that it is good for me. Rustling of papers, and creaking of seats is a sign that time is up.

In the lasts posts I talked about a Bayesian agent in a stationary environment. The flagship example was tossing a coin with uncertainty about the parameter. As time goes by, he learns the parameter. I hinted about the distinction between `learning the parameter’, and `learning to make predictions about the future as if you knew the parameter’. The former seems to imply the latter almost by definition, but this is not so.

Because of its simplicity, the i.i.d. example is in fact somewhat misleading for my purposes in this post. If you toss a coin then your belief about the parameter of the coin determines your belief about the outcome tomorrow: if at some point your belief about the parameter is given by some then your prediction about the outcome tomorrow will be the expectation of . But in a more general stationary environment, your prediction about the outcome tomorrow depends on your current belief about the parameter and also on what you have seen in the past. For example, if the process is Markov with an unknown transition matrix then to make a probabilistic prediction about the outcome tomorrow you first form a belief about the transition matrix and then uses it to predict the outcome tomorrow given the outcome today. The hidden markov case is even more complicated, and it gives rise to the distinction between the two notions of learning.

The formulation of the idea of `learning to make predictions’ goes through merging. The definition traces back at least to Blackwell and Dubins. It was popularized in game theory by the Ehuds, who used Blackwell and Dubins’ theorem to prove that rational players will end up playing approximate Nash Equilibrium. In this post I will not explicitly define merging. My goal is to give an example for the `weird’ things that can happen when one moves from the i.i.d. case to an arbitrary stationary environment. Even if you didn’t follow my previous posts, I hope the following example will be intriguing for its own sake.

About a year ago, I chanced to remark upon the state of Intermediate Micro within the hearing of my colleagues. It was remarkable, I said, that the nature of the course had not changed in half a century. What is more, the order in which topics were presented was mistaken and the exercises on a par with Vogon poetry, which I reproduce below for comparison:

“Oh freddled gruntbuggly,

Thy micturations are to me

As plurdled gabbleblotchits on a lurgid bee.

Groop, I implore thee, my foonting turlingdromes,

And hooptiously drangle me with crinkly bindlewurdles,

Or I will rend thee in the gobberwarts

With my blurglecruncheon, see if I don’t!”

The mistake was not to think these things, or even say them. It was to utter them within earshot of one’s colleagues. For this carelessness, my chair very kindly gave me the chance to put the world to rights. Thus trapped, I obliged. I begin next week. By the way, according to Alvin Roth, when an ancient like myself chooses to teach intermediate micro-economics it is a sure sign of senility.

What do I intend to do differently? First, re order the sequence of topics. Begin with monopoly, followed by imperfect competition, consumer theory, perfect competition, externalities and close with Coase.

Why monopoly first? Two reasons. First it involves single variable calculus rather than multivariable calculus and the lagrangean. Second, student enter the class thinking that firms `do things’ like set prices. The traditional sequence begins with a world where no one does anything. Undergraduates are not yet like the white queen, willing to believe 6 impossible things before breakfast.

But doesn’t one need preferences to do monopoly? Yes, but quasi-linear will suffice. Easy to communicate and easy to accept, upto a point. Someone will ask about budget constraints and one may remark that this is an excellent question whose answer will be discussed later in the course when we come to consumer theory. In this way consumer theory is set up to be an answer to a challenge that the students have identified.

What about producer theory? Covered under monopoly, avoiding needless duplication.

Orwell’s review of Penguin books is in the news today courtesy of Amazon vs Hachette. You can read here about that here. I wish, however, to draw your attention to an example that Orwell makes in his review:

It is, of course, a great mistake to imagine that cheap books are good for the book trade. Actually it is just the other way around. If you have, for instance, five shillings to spend and the normal price of a book is half-a-crown, you are quite likely to spend your whole five shillings on two books. But if books are sixpence each you are not going to buy ten of them, because you don’t want as many as ten; your saturation-point will have been reached long before that. Probably you will buy three sixpenny books and spend the rest of your five shillings on seats at the ‘movies’. Hence the cheaper the books become, the less money is spent on books.

Milton Friedman in his textbook Price Theory, as an exercise, asks readers to analyze the passage. He does not explicitly say what he is looking for, but I would guess this: what can you say about the preferences for such a statement to be true. Its a delightful question. A budget line is given and a point that maximizes utility on the budget lie is identified. Now the price of one of the goods falls, and another utility maximizing point is identified. What kind of utility function would exhibit such behavior?

By the way, there are 60 pence to a shilling and a half a crown is six pennies.

The news of Stanley Reiter’s passing arrived over the weekend. Born in a turbulent age long since passed, he lived a life few of us could replicate. He saw service in WW2 (having lied about his age), and survived the Battle of the Bulge. On the wings of the GI bill he went through City College, which in those days, was the gate through which many outsiders passed on their way to the intellectual aristocracy.

But in the importance and noise of to-morrow

When the brokers are roaring like beasts on the floor of the Bourse

Perhaps a minute to recall to what Stan left behind.

Stan, is well known of his important contributions to mechanism design in collaboration with Hurwicz and Mount. The most well known example of this is the notion of the size of the message space of a mechanism. Nisan and Segal pointed out the connection between this and the notion of communication complexity. Stan would have been delighted to learn about the connection between this and extension complexity.

Stan was in fact half a century ahead of the curve in his interest in the intersection of algorithms and economics. He was one of the first scholars to tackle the job shop problem. He proposed a simple index policy that was subsequently implemented and reported on in Business Week: “Computer Planning Unsnarls the Job Shop,” April 2, 1966, pp. 60-61.

In 1965, with G. Sherman, he proposed a local-search algorithm for the TSP (“Discrete optimizing”, SIAM Journal on Applied Mathematics 13, 864-889, 1965). Their algorithm was able to produce a tour at least as good as the tours that were reported in earlier papers. The ideas were extended with Don Rice to a local search heuristic for non-concave mixed integer programs along with a computation study of performance.

Stan was also remarkable as a builder. At Purdue, he developed a lively school of economic theory attracting the likes of Afriat, Kamien, Sonnenschein, Ledyard and Vernon Smith. He convinced them all to come telling them Purdue was just like New York! Then, to Northwestern to build two groups one in the Economics department and another (in collaboration with Mort Kamien) in the business school.

The Fields medals will be awarded this week in Seoul. What does the future hold for the winners? According to Borjas and Doran, declining productivity caused by a surfeit of dilettantism. The data point to a decline in productivity. By itself this is uninteresting. Perhaps all those on the cusp of 40, see a decline in productivity. What Borjas and Doran rely on is a degree of randomness in who gets a medal. First, there is the variation in tastes of the selection committee (Harish Chandra, for example, was eliminated on the grounds that one Bourbaki camp follower sufficed). Second, the arbitrary age cutoff (the case of the late Oded Schramm is an example of this). Finally, what is the underlying population? Borjas and Doran argue that by using a collection of lesser prizes and honors one can accurately identify the subset of mathematicians who can be considered potential medalists. These are the many who are called, of which only a few will be chosen. The winners are compared to the remaining members of this group. Here is the conclusion (from the abstract):

We compare the productivity of Fields medalists (winners of the top mathematics prize) to that of similarly brilliant contenders. The two groups have similar publication rates until the award year, after which the winners’ productivity declines. The medalists begin to `play the field,’ studying unfamiliar topics at the expense of writing papers.

The prize, Borjas and Doran suggest, like added wealth, allows the winners to consumer more leisure in the sense of riskier projects. However, the behavior of the near winners is a puzzle. After 40, the greatest prize is beyond their grasp. One’s reputation has already been established. Why don’t they `play the field’ as well?

A Bayesian agent is observing a sequence of outcomes in . The agent does not know the outcomes in advance, so he forms some belief over sequences of outcomes. Suppose that the agent believes that the number of successes in consecutive outcomes is distributed uniformly in and that all configuration with successes are equally likely:

for every where .

You have seen this belief already though maybe not in this form. It is a belief of an agent who tosses an i.i.d. coin and has some uncertainty over the parameter of the coin, given by a uniform distribution over .

In this post I am gonna make a fuss about the fact that as time goes by the agent learns the parameter of the coin. The word `learning’ has several legitimate formalizations and today I am talking about the oldest and probably the most important one — consistency of posterior beliefs. My focus is somewhat different from that of textbooks because 1) As in the first paragraph, my starting point is the belief about outcome sequences, before there are any parameters and 2) I emphasize some aspects of consistency which are unsatisfactory in the sense that they don’t really capture our intuition about learning. Of course this is all part of the grand marketing campaign for my paper with Nabil, which uses a different notion of learning, so this discussion of consistency is a bit of a sidetrack. But I have already came across some VIP who i suspect was unaware of the distinction between different formulations of learning, and it wasn’t easy to treat his cocky blabbering in a respectful way. So it’s better to start with the basics.

The August 3rd NY Times has an article about the advertising of Fishoil and Facebook. As sometimes happens with a NYT article, the interesting issues are buried beneath moderately interesting anecdotes that may be traded with others at the dinner table in what passes for serious discussion.

The story is about a company called MegaRed, that peddles fish oil. It wants to target consumers who are receptive to the idea of fish oil because they believe that it confers health benefits. The goal is to get them to try out and perhaps switch to MegaRed.

Facebook proposes a campaign which raises the eyebrows of the marketing director, J. Rodrigo:

“I can go to television at a quarter the price.”

Brett Prescott of Facebook agrees, that yes, Facebook is more expensive than TV. But offers an analogy between advertising on Facebook and firing a shotgun.

“And you are firing that buckshot knowing where every splinter of that bullet is landing.”

If biology is the study of bios, life, and geology is the study of goes, the earth, what does that make analogy?

Some arithmetic to clarify matters. Suppose 1 in 100 of all people would be receptive to the idea of MegaRed’s message. Suppose each of these people is worth $1 on average to MegaRed. If you could reach all 100 of these people via TV, then MegaRed should pay no more than 10 cents per person and so $1 in total.

Enter, stage left, Facebook. It claims that it can target its ads so that they go just to the right person. How much is that worth? $1. In this example, Facebook is no better or worse than TV.

If Facebook has any added value compared to TV it does *not* come from better targeting because one can always compensate for that by paying TV less and reaching more eyeballs. It must come from access to eyeballs unreachable via TV, or, identifying eyeballs that MegaRed would not initially have identified as receptive to their message, or that the medium itself is more persuasive than TV. Is this true for Facebook? If not, MegaRed is better off with TV.

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