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Recently, I thought about submitting a paper to Journal of Monetary Economics. Upon reading its submission guideline, I learned that they charge a submission fee of USD 350, which I found quite expensive.
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As I am preparing for my first teaching assignments at Emory, I started from creating a syllabus template. My department provided a Word template, which was not exactly to my taste, so I wrote a template in \(\LaTeX\) here. The version titled syllabus_template.tex follows the basic structure of the Emory economics template, and the version titled syllabus_template_toda.tex adds some of my information that I use across all my courses. A few comments:
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The compensation at University of California has just published the figures for 2023. I have updated the data set for my paper and run regressions. In case readers are interested in predicting their salaries, the prediction equation in 2023 is \[\log y = 12.12 -0.0100T + 0.0052N_\textrm{pub} + 0.0204N_\textrm{top5} + 0.2485D_\textrm{assoc} + 0.5048D_\text{full}, \] where \(y\) is the 9-month salary, \(T\) is the number of years elapsed since obtaining Ph.D., \(N_\textrm{pub}\) is the cumulative number of peer-reviewed research articles, \(N_\textrm{top5}\) is the cumulative number of top 5 publications, and \(D_\textrm{assoc}, D_\textrm{full}\) are dummy variables for associate and full professors.
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Three years ago, I wrote a blog post in which I mentioned that I stopped (strictly speaking, significantly reduced) contributing in 403(b) and 457(b) retirement savings plans because I could no longer afford it.
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Jianjun Miao of Boston University and Pengfei Wang of Peking University published a paper titled “Asset Bubbles and Credit Constraints” at American Economic Review in 2018. In their abstract, they state that they “provide a theory of rational stock price bubbles”. For those who are not familiar with the economic theory of bubbles, “rational bubble” means that the asset price (denoted by \(P\)) exceeds its fundamental value (denoted by \(V\)) defined by the present value of dividends, so \(P>V\), in a model in which agents are rational.
Most papers in the rational bubble literature assume that the asset pays no dividends, because there are known difficulties with positive dividends. (I can talk about this more but it is technical, so I refer the reader to my JME review article with Tomohiro Hirano, especially Section 3.4.) Miao and Wang’s paper is ambitious because they claim to attach a rational bubble to a dividend-paying asset. For instance, in their literature review, they state
Some studies (e.g., Scheinkman and Weiss 1986; Kocherlakota 1992, 2008; Santos and Woodford 1997; Hellwig and Lorenzoni 2009) have found that infinite-horizon models of endowment economies with borrowing constraints can generate rational bubbles. Unlike this literature, our paper analyzes a production economy with stock price bubbles attached to productive firms.
Here the cited papers are all rational bubble models. Subsequent papers by the authors also advertise Miao and Wang (2018) as a rational bubble model. For example, Footnote 4 of Dong, Miao, and Wang (2020) states
Introducing dividends or rents will complicate our analysis without changing our key insights. See Miao and Wang (2018) and Miao, Wang, and Xu (2015) for models of rational bubbles attached to assets with dividends or rents.
In a recent working paper by Tomohiro and I titled “Rational Bubbles: A Clarification”, we mathematically proved the nonexistence of rational bubbles in the model of Miao and Wang (2018). In other words, \(P=V\) in their model.
It seems that there is a widespread misunderstanding in the literature. According to our systematic literature search detailed in the paper, there are 74 papers that are mainly about the theory of bubbles and cite Miao and Wang (2018) as a paper on bubbles. Among those 74 papers, 68 cite Miao and Wang (2018) as a rational bubble model specifically. As proved in our paper, the model of Miao and Wang (2018) is not a rational bubble model. It is an asset pricing model with multiple equilibria, where the high- or low-stock price equilibrium is selected based on agents’ self-fulfilling expectations. In both equilibria, the stock price reflects fundamentals. I hope that our paper will help to reach a better and mutual understanding about bubbles, and that the science of bubbles will prosper forever, without ever imploding.
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I have been investing in Roth IRA. Currenty the contribution limit is $7,000/year.
I haven’t been paying attention much, but there are income limits for traditional and Roth IRA. For traditional, married couples filing jointly cannot deduct contributions if their modified adjusted gross income (MAGI) is above $136,000. For Roth, married couples filing jointly cannot contribute if their MAGI is above $240,000.
Because I recently got a raise by changing employer, I can no longer contribute to Roth. However, there is a legal loophole called backdoor Roth. All you need is to contribute to a traditional IRA (which is not tax deductible due to the income limit but this is irrelevant) and then do a Roth conversion. This way, anybody can contribute to Roth regardless of their income. So from next year on, I can simply contribute $7,000 of cash to my traditional IRA account, do a Roth conversion, and invest the funds in whatever way I like.
However, for this year there is a problem because I have already contributed to Roth before I knew I would exceed the income limit. I did a bit of research and found this article. Reading it, I did the following.
The idea is that, by recharacterizing my existing Roth contributions to traditional, it’s as if I contributed to traditional in the first place. To save my mental resource, I added sufficient cash to hit the $7,000 annual contribution limit right away so that I can forget about it for this year. Because the existing contributions to Roth had capital gains, by recharacterizing to traditional, I will have to pay capital gains taxes. This TurboTax article explains how to handle taxes.
It’s fun to learn something new about money tips, but I spent a few hours of my time doing so. Since the income limit for Roth is not binding due to the backdoor Roth loophole, it would make more sense for the government to simply eliminate the income limit for Roth altogether. And if there is no income limit for Roth, there should be no limit for traditional either. Our lives will be much simpler that way.
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As I have already announced on my website, I am resigning from UCSD. Today is my last day. I have been employed for 11 years, so I have bittersweet feelings for sure.
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I have just returned from a 10-day trip to Japan. During this short stay, I went to the Ikaho hot spring, did some sightseeing in Tokyo with my family, and gave talks at Waseda University and University of Tokyo.
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I presented my paper “Housing Bubbles with Phase Transitions” at the UCSD Friday faculty seminar. Because this was my last talk at UCSD, I gave the following speech.
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After spending several days, I significantly updated my website. Below is a list of main changes.
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Maybe it is not the best use of my time but I created a “Talks” page, which lists past and future talks and presentations. After spending all afternoon tweaking the code, I created something satisfactory. For now I included only talks in 2023 and 2024 but I might add past ones.
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I finished writing the draft of my forthcoming textbook “Essential Mathematics for Economics”. The book is based on my math camp teaching material. Please let me know if you have any comments on the draft.
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I am still waiting for the replacement battery for my 2016 Nissan Leaf. It’s nearly 9 months wait now.
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In 2016 I purchased a Nissan Leaf. Given the technological progress in electric vehicles, now it’s almost a joke but it had a 30kWh battery with around 110 miles of range. Including everything (tax, registration, etc.), it cost 44,142 dollars. My employer subsidized 10,000 and I received 7,500 federal and 2,500 state tax credits, so at that time I thought it was not a bad deal. 110 miles of range seemed enough to do daily chores, and for road trips we had been renting a gas-powered vehicle. This was our only vehicle in the household until 2020, when we bought a Tesla Model Y.
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For managing a bibliography for my papers, for a long time I have been using the natbib package with bibtex to compile. ``` \usepackage[authoryear,round]{natbib} \usepackage{doi}
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When I moved from Connecticut to San Diego in 2013, one thing I paid attention to when searching for a house was to find one within reasonable distance from work. I knew that San Diego has nice weather and commuting by bicycle was feasible. So to save money and get some exercise, I cut the number of vehicles in my household from two to one and bought an electric bike to commute. (In 2020, I went back to two vehicles because we could no longer keep up with only one vehicle to manage kids’ activities.)
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It was reported that Wimbledon will ban Russian (and Belarusian) players because of Russian’s invasion of Ukraine.
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Since I started working in 2013, I haven’t thought much about investment. Because I know that investing in an index fund is the theoretically right thing to do and I do not like paying taxes, in addition to participating in my employer’s mandatory defined benefit retirement plan, I have just been maxing out investment in 403(b), 457(b), and Roth IRA (all invested in low cost index funds).
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This post is completely boring for outsiders. I am just writing this down so that I do not forget.
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My university uses Canvas for instructional purposes. Canvas has a functionality called “Inbox”, which allows you to send messages. I have long thought this functionality not only useless but even harmful. This is because I ignore everything sent to Canvas Inbox, but students who are not aware that I do not use Canvas Inbox may send me messages that gets ignored and may complain. Since I was not able to find information on how to disable Inbox, I contacted the university technical support.
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I have been a long time customer of Shan Xi Magic Kitchen, which is a Chinese restaurant in San Diego that serves Shan Xi food.
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These days I mostly play competitive tennis, so my opponents usually have sufficient understandings of the rules and we do not get into disputes. However, debates and disputes sometimes occur in recreational play, which could be annoying. So in a series of posts, let me talk about some rules that could be overlooked by recreational players. The official rules can be found in the “Friend at Court” here.
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These days I mostly play competitive tennis, so my opponents usually have sufficient understandings of the rules and we do not get into disputes. However, debates and disputes sometimes occur in recreational play, which could be annoying. So in a series of posts, let me talk about some rules that could be overlooked by recreational players. The official rules can be found in the “Friend at Court” here.
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These days I mostly play competitive tennis, so my opponents usually have sufficient understandings of the rules and we do not get into disputes. However, debates and disputes sometimes occur in recreational play, which could be annoying. So in a series of posts, let me talk about some rules that could be overlooked by recreational players. The official rules can be found in the “Friend at Court” here.
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My paper “Capital and Labor Income Pareto Exponents across Time and Space” got accepted at Review of Income and Wealth. I have long felt that in the discussion of inequality, people often don’t make the distinction between income and wealth. In this paper we (my coauthor Tjeerd de Vries and I) estimate the Pareto exponents for capital and labor income separately for as many countries/years as possible. Using 475 country-year observations, we find that the median capital and labor income Pareto exponents are 1.46 and 3.35 respectively, so capital income (hence wealth) is more unequal than labor income. This conclusion is not surprising at all, but the point of the paper is to provide a systematic analysis, which was lacking in the earlier literature.
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My paper “Asymptotic Linearity of Consumption Functions and Computational Efficiency” with Qingyin Ma got accepted at Journal of Mathematical Economics. The main result is that when the marginal utility function is regularly varying (behave like a power function), the consumption function in optimal savings problem becomes asymptotically linear and we characterize the asymptotic slopes. Initially this paper was part of a bigger project with Ma & Toda (2021), but we split the paper in two to keep them focused and at manageable lengths. The JET paper treats only the case with CRRA (constant relative risk aversion) utility but has an economic application. The JME paper assumes regular variation plus some technical condition and discusses computational efficiency.
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I played the San Diego District Championship NTRP 3.5 men’s singles over the last two weekends, and I won the final 6-1, 6-7(5-7), 7-5.
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My paper “Perov’s Contraction Principle and Dynamic Programming with Stochastic Discounting” got accepted at Operations Research Letters. I found a generalization of Banach’s contraction mapping theorem when I was studying a certain dynamic programming problem with stochstic discounting. It turned out that the fixed point theorem was due to Perov (1964) but I thought the application was interesting, so I wrote a short paper.
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In tennis, a pusher is a player who can consistently hit the ball back inside the opponent’s court. They have good footwork and run to every ball. Michael Chang and Rafael Nadal are legendary professional players that have perfected this valuable skill.
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I have been playing tennis and publishing papers long enough that I have found something in common.
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I have been a customer of American Home Shield, a home warranty company, for a few years until today.
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I have been a recreational tennis player for 6 or 7 years. Since fall 2020, I have started to play some matches. (You can see my statistics here.) After starting to play competitively, I have read a lot about tennis strategies because obviously it is more fun to win than to lose. I soon learned (both from theory and experience) that one of the easiest ways to improve your match results is to be more consistent, that is, to reduce unforced errors. So I have been paying attention to consistency and my games have improved.
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I don’t remember when I opened a ResearchGate account; I guess I did so to increase the visibility of my research. I don’t really use their service, but I find it annoying that I get requests to upload full-text articles. This is a waste of time because most of my papers are available online as working paper versions. (These days I upload my working papers exclusively to arXiv.) So I decided to write a short document stating that all of my papers are linked from my personal website (and provided the link), and uploaded it as a full-text article.
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It is a great honor to announce that I have been awarded the 4th Government Pension Investment Fund (GPIF) Finance Award under the auspices of Ministry of Health, Labor and Welfare and Ministry of Education, Culture, Sports, Science and Technology in Japan. I am very happy that my research has been recognized.
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My paper “A Theory of the Saving Rate of the Rich” was accepted at Journal of Economic Theory. I started this project in early 2020. Initially, the paper was about rigorously establishing the asymptotic linearity of policy functions when preferences are homothetic and the constraint is asymptotically homogeneous of degree 1. This is not surprising but the proof is difficult. As we worked on the proof, we (my coauthor and I) discovered that the asymptotic slope of the policy function can be zero, which was surprising. When the asymptotic marginal propensity to consume (MPC) is zero, an infinitely wealthy agent saves 100% of the wealth, which can explain the empirical puzzle that wealthy people save a lot although it seems unnecessary. So instead of focusing on just a mathematical fact, we decided to frame the paper as a new theory of the saving rate of the rich.
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I have been investing for over 20 years. After learning about the capital asset pricing model and the mutual fund theorem and reading “A Random Walk Down Wall Street” and “Stocks for the Long Run”, I have been more or less consistently investing in low-cost index ETFs such as VTI and VXUS. This allowed me to stay in the market during the bottom in March 2009 and not to miss the bull market since then despite some of my colleagues advising me that stocks are overpriced. My kids’ 529 funds have grown about 3 times in nominal value. I have been maxing out my 403b, 457b, and Roth IRA contributions and joking I could retire if I choose to. Based on theory and experience, I preach the importance of passive investing to students in my finance class.
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My paper “Necessity of Hyperbolic Absolute Risk Aversion for the Concavity of Consumption Functions” was accepted at Journal of Mathematical Economics. The publication process was quite efficient. I came up with the idea in late September 2020 and wrote a short paper. After getting rejected from a different journal, I sent to JME. I am very happy that it came out in less than three months after I have started the project. Journals in economics tend to be very slow in the review process, perhaps because many papers tend to be long and unfocused. We should all write concise and focused papers.
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I have just signed the Great Barrington Declaration.
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Recently, my working paper Susceptible-Infected-Recovered (SIR) Dynamics of COVID-19 and Economic Impact has surpassed my JEBO paper in terms of citation counts, and has become my most cited paper. My COVID-19 paper is one of the very first written by an economist on this topic, and it appeared in the first issue of the working paper series Covid Economics. Although I am no longer working on this paper since the situation with COVID-19 has been changing too quickly (especially when I wrote the paper in March 2020) to keep up with, I am glad that this paper has made some impact. In fact, it was featured in VoxEU and Fortune articles.
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As a long-time California resident, I am very well aware of all those government red tapes. But the recent move of the city of Berkeley to ban placing junk food and beverages at checkout ailes is completely nonsense.
$$..., \[..., and \begin{equation*}... Published:
I have been using \(\LaTeX\) for over 20 years now. When I write a displayed equation without numbering on a single line, I have been using $$...$$ because it was simple. I didn’t understand why some people use \[...\], because the latter takes more time to type and is not necessarily easy to read. Today I read this article and learned that $$...$$ is incorrect. From now on, I will switch to \begin{equation*}...\end{equation*} because it is easy to read and we can add equation numbering by deleting * if we change our mind.
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I have recently read the article “Why Mathematicians Should Stop Naming Things After Each Other”. The same logic seems to apply to economics.
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Let \(A, B\) be square (complex) matrices such that \(|B| \le A\). Then it is well known that \(\rho(B) \le \rho(|B|) \le \rho(A)\), where \(\rho\) denotes the spectral radius (largest absolute value of all eigenvalues). See, for example, Theorem 8.4.5 of Horn and Johnson (2013). In my recent paper with Brendan Beare and Won-Ki Seo, we needed to use the spectral abscissa (largest real part of all eigenvalues) instead of the spectral radius. By analogy, we can make the following conjecture: if \(A, B\) are square complex matrices such that \(\mathrm{Re} b_{nn} \le a_{nn}\) for all \(n\) and \(|b_{nn’}| \le a_{nn’}\) for all \(n \neq n’\), then is it true that \(\zeta(B) \le \zeta(A)\), where \(\zeta\) denotes the spectral abscissa?
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There is a restaurant called “The Bistro” on UCSD campus. Although I don’t like this restaurant because it’s basically a fusion American Asian place, sometimes I have to eat there when we take seminar speakers for lunch. Once I ordered some fried cod (neither quite fish and chips nor tempura). On the menu it said the dish comes with brown rice, so I asked the server to substitute white rice for brown rice. (Although I don’t have statistics to quote, I would say most Japanese people eat white rice - only those that are health-conscious and opinionated eat brown rice, though obviously the latter is healthier.) When the dish arrived, I was stunned that the rice, though white, was sushi rice (i.e., vinegared rice). I asked the server to bring proper white rice but she didn’t know the difference. Since then, whenever I organize the seminar lunch, I choose a different place.
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I have created a new website. I have been using Google Sites to create my old website. I like the classic Google Sites because it allows the user to take control of the structure by programming in html. However, the new Google Sites no longer have this feature, and since the classic Google Sites will be discontinued in 2021, I had to do something else. After a bit of Google search, I found this template, which is exactly what I wanted (ability to take full control, free, no advertisements, etc.).