Teaching

Interpolation Vs Transition

Zachary BartschLeave a comment

Sometimes you read an academic article and the author fills in the data gaps with interpolation. That is, they assume some functional form of the data and then replace the missing values with the estimated ones. Often, lacking an informed opinion about functional form, authors will just linearly interpolate between the closest known values. Sometimes this method is OK. But sometimes we can do better.

Historical census data provides a good example because the frequency was only every ten years. Say that we want to know more about child migration patterns between 1850 and 1860. What happened in the intervening years? Who knows. Let’s look at the data.

Using data on individuals who have been linked across censuses allows us to fill in the gaps a little bit. For simplicity, let’s just look at whether a child migrant lived in an urban location and whether they lived on a farm. That means that there are 4 possible ways to describe their residence. Below is a summary of where children migrants lived at the age of zero in 1850 and where the same children lived a decade later at the age of ten in 1860 given that they moved counties.

When I’m the mean time did these children move from one place and to the other? We don’t know exactly. The popular answer is to say that they moved uniformly throughout the decade. That’s ‘fine’. But it assumes that the rate at which people departed places was rising and the rate at which they arrived places was falling. Maybe that’s true, but we don’t really know. Below-left is a graph that shows the linear interpolation.

The nice thing about linear interpolation is that everyone is accounted for at each point in time. The total number of people don’t rise or fall in the intervening interpolation period. But if we were to assume that children departed/arrived at each type of place at a constant rate (maybe a more reasonable assumption), then suddenly we lose track of people. That is, the sum of people dips below 100% as people depart faster than they arrive.

What’s the alternative to linear interpolation?

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Life Tables are Cool

Zachary BartschLeave a comment

Demography is cool generally, but life tables are really cool in their elegance. Don’t know what a life table is? Let me ‘splain.

A life table uses data from private or public death registers, or even genealogical records, to identify a variety of survival and death estimates. Briefly, the tables include for each age:

  • Probability of death in the next year
  • Probability of surviving to the age
  • The life expectancy

There is more in the tables, but these are the big items that people often want to know. All of the various table columns can be calculated from survival rates. The US government and the UN each has created many such tables for a variety of time, locations, and development details. For example, the earliest and most dependable one is from 1901 and includes separate tables by race, sex, migrant status, urbanity, and even for some specific states.

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Confronting my Macroeconomics Professor

Joy BuchananLeave a comment

I’m gearing up to teach macroeconomics for the first time. The following is a story that I will keep in mind as I work to make technical material relevant to undergraduates.

Years ago, I was an undergraduate sitting in a macroeconomics class. As it happened, I was in an intermediate-level macro class with no relevant background or context for the material. (If I had taken principles-level econ, then maybe I wouldn’t have been in this situation.)

My instructor was grinding through theory in a methodical way. By the end of the first month, as I remember it, we had covered the short run and the medium-term effects of monetary policy.

For anyone who is not familiar, see these MRU videos on shifting the aggregate supply curve.

“The Short-Run Aggregate Supply Curve“

“Office Hours: Using the AD-AS Model“

In summary, the government can inject money into the economy to achieve a short-term increase in output. For a short amount of time, you can help, and that seemed good to me. I had signed up for the course to understand how to reduce poverty and make the world better. I was acing the exams. Things were going well at first.

Then we got bad news. Increasing the money supply does not work for long. Consumers realize that everything is more expensive, so they cut back on real spending. The economy shifts back to where it was before. Nothing actually improves. I had spent a month of my life on this class and we were getting nowhere.

After the lecture on returning to the long-run aggregate supply curve, I went up to the professor after class. I asked him what was going on and when would we learn something that matters. (I was polite. I realized I was going to sound dumb to him, but life is short. I needed to know if this class was going to deliver anything.)

He looked at me, surely confused that I was unsatisfied with the standard progression of material in his course. Then he explained, “Oh. You are talking about the long term, and we will get to that next month.” That’s what I needed. I did not drop the course or the major. I’m an economics professor today because I didn’t mind looking like an idiot if I could get my questions answered.

This story helps me remember what it was like to be an undergrad in an economics class. Tyler says “context is that which is scarce.” Economics teachers need to do two things at once: present technical material and provide context. I will try to get that mix right going forward.

Note to students: Students, don’t be afraid to ask stupid questions. This is your chance. A good teacher will be glad you took the initiative. However, if the question occurs to you right in the middle of a lecture, then it may or may not be the appropriate time for the lecturer to stop and have a conversation with you. Teachers will be most amenable to having a deep conversation after class or during office hours.

My macro-related research:

Published paper: “If Wages Fell During a Recession” YouTube video presentation of this paper from minute 19:00-32:00.

Working paper (no draft yet): “Sticky Prices as Coordination Failure: An Experimental Investigation”

5 Game Theory Course Changes

Zachary Bartsch1 Comment

I want to share some changes that I’ll make to my game theory course, just for the record. It’s an intense course for students. They complete homeworks, midterm exams, they present scholarly articles to the class, and they write and present a term paper that includes many parts. Students have the potential to learn a huge amount, including those more intangible communication skills for which firms pine.

There is a great deal of freedom in the course. Students model circumstances that they choose for the homeworks, and they write the paper on a topic that they choose. The 2nd half of the course is mathematically intensive. When I’ve got a great batch of students, they achieve amazing things. They build models, they ask questions, they work together. BUT, when the students are academically below average, the course much less fun (for them and me). We spend way more time on math and way less time on the theory and why the math works or on the applicable circumstances. All of that time spent and they still can’t perform on the mathematical assignments. To boot, their analytical production suffers because of all that low marginal product time invested in math. It’s a frustrating experience for them, for me, and for the students who are capable of more.

This year, I’m making a few changes that I want to share.

  1. Minimal Understanding Quizzes: All students must complete a weekly quiz for no credit and earn beyond a threshold score in order to proceed to the homework and exams. I’m hoping to stop the coasters from getting ‘too far’ in the course without getting the basics down well enough. The quizzes must strike the balance of being hard enough that students must know the content, and easy enough that they don’t resent the requirement.
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5 Easy Steps to Improve Your Course Evals.

Zachary Bartsch2 Comments

Incentives matter. I’ve taught at both public and private universities, and students have given me both great course evaluations and less great student evaluations. The private university cared a lot more about them. Obviously, some parts of student evaluations of their instructors are beyond the instructor’s control. The instructor can’t control inalienables and may not be able to change their charisma. But what about the things that instructors can control? Regardless of your current evals, here are 5 policies that are guaranteed to improve your course evaluations.

1: Very Clear Expectations/Schedule

Have all deadlines determined by the time that the semester starts. Students are busy people and they appreciate the ability to optimally plan their time. Relatedly, students desire respect from their instructor. Having clear rubrics and deadlines helps students know your expectations and how to meet them – or at least understand how they failed to meet them. Students want to feel like they were told the rules of the game ahead of time. This means no arbitrary deductions or deadlines. The syllabus is a contract if you treat it like one.

2: Mid-Semester Evaluations

One of the absolute best ways to improve your evaluation is to ask your evaluators for a performance update. Make a copy of your end-of-semester course evaluation and issue it about halfway through the semester. Then, summarize the feedback and review it with your class. This achieves three goals. (1) It is an opportunity to clarify policy if there are misplaced complaints. You may also wish to explain why policy is what it is. Knowing a good reason makes students more amenable to policies that they otherwise don’t prefer.  (2) It provides voice to students who have things to say. Often, students want to be heard and acknowledged. It’s better that a student vents during the informal mid-semester survey than on the important one at the conclusion of the course. (3) If there are widespread issues with your course, then make changes. If you’re on the fence about something, then take a poll. And if you decide to make changes, then be graciously upfront about it. Unexplained or covert changes violate policy #1.

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Supply & Demand, with Tables?

Zachary Bartsch2 Comments

When I was a graduate student, I paid for my tuition by tutoring for the university athletics department. I tutored stat, math, micro, macro, excel, and finance. I tutored the same students each week, so I got to know them pretty well over the course of the semester. I also got to know their strengths and weaknesses. It was at this time that I realized most quantitative or even analytical ideas could be described in 4 potentially equivalent ways:

  1. Mathematically
  2. Using logic in English
  3. Graphically
  4. With a Table

In this post I want to share the Supply & Demand cheat-sheet that I use to help my students learn about the effects of supply and demand.

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The Value of Student Organizations and On-Campus Education: Anecdotal Evidence from Tim Keller

Joy Buchanan6 Comments

Tim Keller, who was the founding pastor of Redeemer Presbyterian Church in New York City, died last week. Starting and growing a church in Manhattan takes talent. I am reading Tim Keller’s biography by Collin Hansen through the lens of Tyler’s Talent book.

How did a successful leader and famous speaker get started? Keller is not described in the book as an outgoing child. Although academically gifted, “He grew up socially awkward, a wallflower…”

In 1968, Keller started at Bucknell University. Keller, who would go on to write multiple best-selling books, may have refined some of his writing skills through his coursework. From my reading, the most important aspect of his college experience was not the classes but the chance to be a leader of a campus (religious) club and having so many peers close by to practice “working” with. “Some 2,800 students lived within short walking distance of each other…[on campus].”

He planned retreats and invited famous guest speakers who appealed to his audience. He got feedback on the effectiveness of different messages and programs. Due to Keller’s efforts, the college club chapter meetings more than doubled in size. You can see the beginnings of the man who would go on to manage a large organization and attract over 5,000 people to hear him on the Sunday after 9/11.

In the debate over the value of a college education, the value of the experience students gain from holding officer positions in campus clubs is underrated. The information or credentials that can be obtained through online classes doesn’t build this kind of social capital. For leaders of organizations, college clubs are how some of them gained momentum and developed confidence.

Students can learn in a low stakes environment. For example, an ambitious club president can get 20 students to show up for pizza instead of 8. Club leaders get to make the key decisions and solve the problems that determine the success of their organization, because the faculty are too busy to micromanage club meetings. This gives students accurate feedback on the success of their own ideas.

In-person campus-based education is more than acquiring knowledge from textbooks. It is a dynamic environment in which students can develop social skills and form their network for future professional support. By participating in these organizations, students learn collaboration, decision-making, problem-solving, and mentoring — skills that are transferable across various domains of life.  

Beware of Scatterplots

Zachary BartschLeave a comment

Scatterplots are a great investigatory tool. You can scatterplot raw data for two variables and, if the relationship is strong, then you can see the functional form that relates x and y (linear, polynomial, exponential, etc.). However, there are two data characteristics that are a scatterplots Achilles’ heel: large samples and discrete variables. And they create misleading scatterplots for the same reason.

Examine the below scatterplots for y vs the discrete variables x1, x2, & x3 on the interval [0,10]. What do you think slopes or correlations are?

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Steal My Paper Ideas!

James Bailey2 Comments

Since early in graduate school I’ve kept a running list of ideas for economics papers I’d like to write and publish some day. I’ve written many of the papers I planned to, and been scooped on others, but the list just keeps growing. As I begin to change my priorities post-tenure, I decided it was time to publicly share many of my ideas to see if anyone else wants to run with them. So I added an ideas page to my website:

Steal My Paper Ideas! I have more ideas than time. The real problem is that publishing papers makes the list bigger, not smaller; each paper I do gives me the idea for more than one new paper. I also don’t have my own PhD students to give them to, and don’t especially need credit for more publications. So feel free to take these and run with them, just put me in the acknowledgements, and let me know when you publish so I can take the idea off this page.

Here’s one set of example ideas:

State Health Insurance Mandates: Most of my early work was on these laws, but many questions remain unanswered. States have passed over a hundred different types of mandated benefits, but the vast majority have zero papers focused on them. Many likely effects of the laws have also never been studied for any mandate or combination of mandates. Do they actually reduce uncompensated hospital care, as Summers (1989) predicts? Do mandates cause higher deductibles and copays, less coverage of non-mandated care, or narrower networks? How do mandates affect the income and employment of relevant providers? Can mandates be used as an instrument to determine the effectiveness of a treatment? On the identification side, redoing older papers using a dataset like MEPS-IC where self-insured firms can be used as a control would be a major advance.

You can find more ideas on the full page; I plan to update to add more ideas as I have them and to remove ideas once someone writes the paper.

Thanks to a conversation with Jojo Lee for the idea of publicly posting my paper ideas. I especially encourage people to share this list with early-stage PhD students. It would also be great to see other tenured professors post the ideas they have no immediate plans to work on; I’m sure plenty of people are sitting on better ideas than mine with no plans to actually act on them.

New Textbook for Game Theory and Behavioral Economics

Joy BuchananLeave a comment

Game Theory and Behavior is extremely readable. Carpenter and Robbett have a great set of examples (e.g. the poison drink dilemma from The Princess Bride). I think the book has been developed from teaching a course that resonates with undergraduates today. The authors are both experimental economists, so there is natural integration with lab results from experiments with games.

Topics covered include:

Game Theory and standard definitions

Solving Games

Sequential Games

Bargaining

Markets

Social Dilemmas

Voting

Behavioral Extensions of Standard Theory

In their words:

This book provides a clear and accessible formal introduction to standard game theory, while at the same time addressing how people actually behave in these games and demonstrating how the standard theory can be expanded or updated to better predict the behavior of real people. Our objective is to simultaneously provide students with both the theoretical tools to analyze situations through the logic of game theory and the intuition and behavioral insights to apply these tools to real world situations. The book was written to serve as the primary textbook in a first course in game theory at the undergraduate level and does not assume students have any previous exposure to game theory or economics. 

Not every book on game theory would be described as extremely readable. The authors do present mathematical concepts and solutions and practice problems. I want to be clear that I’m not implying that their book is not rigorous. They present game theory as primarily an intuitive and important framework for decisions instead of as primarily a mathematical object, which should go over well with most undergraduate students.

The following are questions that occurred to me as I was writing this post, with ChatGTP replies.