Winner of the New Statesman SPERI Prize in Political Economy 2016

Monday 9 April 2012

Microfoundations and Evidence (1): the street light problem

                One way or reading the microfoundations debate is as a clash between ‘high theory’ and ‘practical policy’. Greg Mankiw in a well known paper talks about scientists and engineers. Thomas Mayer in his book Truth versus Precision in Economics (1993) distinguishes between ‘formalist’ and ‘empirical science’. Similar ideas are perhaps behind my discussion of microfoundations and central bank models, and Mark Thoma’s discussion here.
                In these accounts, ‘high theory’ is potentially autonomous. The problem focused on is that this theory has not yet produced the goods as far as policy is concerned, and asks what economists who advise policy makers should do in the meantime. But the presumption is generally that theory will get there as soon as it can. But will it do so of its own accord? Is it the case that academics are quite good at selecting what the important puzzles are, or do they need others more connected to the data to help them?
                There is a longstanding worry that some puzzles are selected because they are relatively easy to solve, and not because they are important. Like the proverbial person looking under the street light for their keys that they lost somewhere less well lit. This is the subject of this post. A later post will look at another concern, which is that there may be an ideological element in puzzle selection. In both cases these biases in puzzle selection can persist because the discipline exerted by external consistency is weak.
The example that reminded me about this came from this graph.

US Savings Rate

The role of the savings rate in contributing to the Great Recession in the US and elsewhere has been widely discussed. Some authors have speculated on the role that credit conditions might have played in this e.g. Eggertsson and Krugman here, or Hall here. But what about the steady fall in savings from the early 1980s until the recession?
                Given the importance of consumption in macroeconomics, you would imagine there would be a huge literature, both empirical and theoretical, on this. Whatever this literature concluded, you would also imagine that the key policy making institutions would incorporate the results of this research in their models. Finally you might expect any academic papers that used a consumption model which completely failed to address this trend might be treated with some scepticism. OK, maybe I’m overdoing it a bit, but you get the idea. (There has of course been academic work on trying to explain the chart above: a nice summary by Guidolin and Jeunesse is here. My claim that this literature is not as large as it should be is of course difficult to judge, let alone verify, but I’ll make it nonetheless.)
                It would be particularly ironic if it turned out that credit conditions were responsible for both the downward trend and its reversal in the Great Recession. However that is exactly the claim made in two recent papers, by Carroll et al here and Aron et al (published in Review of Income and Wealth (2011), earlier version here), with the later looking at the UK and Japan as well as the US. Now if you think this is obvious nonsense, and there is an alternative and well understood explanation for these trends, then you can stop reading now. But otherwise, suppose these authors are right, why has it taken so long for this to be discovered, let alone be incorporated into mainstream macromodels?
                Well in the discovery sense it has not. John Muellbauer and Anthony Murphy have been exploring these ideas ever since the UK consumption boom of the late 1980s. As I explained in an earlier post, there was another explanation for this boom besides credit conditions that was more consistent with the standard intertemporal model, but the evidence for this was hardly compelling. The problem might be not so much evidence, as the difficulty in incorporating credit effects of this kind into standard DSGE models. Even writing down a tractable microfounded consumption function that incorporates these effects is difficult, although Carroll et al do present one. Incorporating it into a DSGE model would require endogenising credit conditions by modelling the banking sector, leverage etc . This is something that is now beginning to happen largely as a result of the Great Recession, but before that it was hardly a major area of research.
                So here is my concern. The behaviour of savings in the US, UK and elsewhere has represented a major ‘puzzle’ for at least two decades, but it has not been a major focus of academic research. The key reason for that has been the difficulty of modelling an obvious answer to the puzzle in terms of the microfoundations approach. John Muellbauer makes a similar claim in this paper. To quote: “While DSGE models are useful research tools for developing analytical insights, the highly simplified assumptions needed to obtain tractable general equilibrium solutions often undermine their usefulness. As we have seen, the data violate key assumptions made in these models, and the match to institutional realities, at both micro and macro levels, is often very poor.”
                I do think microfoundations methodology is progressive. The concern is that, as a project, it may tend to progress in directions of least resistance rather than in the areas that really matter – until perhaps a crisis occurs. This is not really mistaking beauty for truth: there are plenty of rather ugly DSGE macro papers out there, one or two of which I have helped write. It is about how puzzles are chosen. When a new PhD student comes to me with an idea, I will of course ask myself is this interesting and important, but my concern will also be whether the student is taking on something where they can get a clear and publishable result in the time available.
When I described the Bank of England’s macromodel BEQM, I talked about the microfounded core, and the periphery equations that helped fit the data better. If all macroeconomists worked for the Bank of England, then that construct contains a mechanism that could overcome this problem. The forecasters and policy analysts would know from their periphery equations where the priority work needed to be done, and this would set the agenda for those working on microfounded theory.
                In the real world the incentive for most academics is to get publications, often within a limited time frame. When the focus of macroeconomic analysis is on internal consistency rather than external consistency, then it is unclear whether this incentive mechanism is socially optimal. If it is not, then one solution is for all macroeconomists to work for central banks! A more realistic alternative might be to reprise within academic macroeconomics a modelling tradition which placed more emphasis on external consistency and less on internal consistency, to work alongside the microfoundations approach. (Justin Fox makes a similar point in relation to financial modelling.)     


  1. Simon
    That savings rate chart tells me that savings is irrelevant but for a reason. Bear with me. It just so happens that savings are aninverse function of debt accumulation, so of course savings will fall steadily for a long time before a crisis. But it is irredentist because you're merely observing a variable ga is a function of the true independent variable - debt accumulation.

  2. Sorry for the typos:
    irredentist = irrelevant
    ga = that

  3. Simple answer: if you increase liquidity constraints, you decrease savings. Shift the tax burden (1981 to some extent, 1983 and especially 1986 in large part) without reducing costs (in many cases, increasing them--Baumol's Law abides) and the ability to save is reduced. (Debt accumulation, pace bjd, is collateral, given a model that allows for borrowing against the future and overoptimistic credit management on the supply side.)

    But that requires noticing that the 1986 Grand Bargain made debt reduction and tertiary education more difficult to achieve for the vast majority of the population, which in turn reduced potential savings, with reality following. And since the 1986 Tax Reallocation Act is sacrosanct, doing research on its negative effects isn't going to happen.

    1. Bingo; I guess I said the same thing below. Make inequality higher and you make savings lower. Simple as that.

  4. The declining savings rate does not strike me as that hard to explain. Over the same period, we have observed an extreme decline in interest rates. There are a variety of policy related reasons for part of that decline involving monetary policy, but the overwhelming majority of the decline is due to the flood of foreign savings from developing economies being made available to firms and consumers in the US for the first time due to globalization.

    The reason most models have trouble explaining this is that most models think of the US as a closed economy.

  5. Yes but the decline in savings is just a bi-product of the more important increase in debt.

  6. “The problem might be not so much evidence, as the difficulty in incorporating credit effects of this kind into standard DSGE models. Even writing down a tractable microfounded consumption function that incorporates these effects is difficult…”

    Isn’t tractability only an issue if you are solving the model in closed form? Why not just make the model very realistic, not worry about mathematical tractability, and then have the computer calculate what happens numerically for various relevant, realistic parameter ranges, and learn from that? You can get a much more realistic model this way.

    I talk about this more at:

  7. I think a huge -- and tragic -- example of looking under the lamp post, and libertarian bias, is how in economics the concern, the goal, is almost always Pareto optimality, rather than total societal utils optimality.

    A big reason given is that it’s hard to measure total societal utils. Well, it’s hard to measure lots of things, so is it then optimal to completely ignore them, and just go 100% with random luck for our optimizing strategy? We can’t improve on that? When you choose a city and a home, do you say it’s hard to estimate the expected utility of a home, so I’ll just throw a dart at a map of the world and decide that way? I’ll put no thought into it whatsoever, and completely ignore the great deal of important information that I do have, and can get? Of course not.

    Clearly, it’s hard to get a more pro-libertarian and anti-utilitarian bias than saying I’ll almost always make Pareto optimality a central focus and almost always completely ignore total societal utilis.

  8. "Now if you think this is obvious nonsense, and there is an alternative and well understood explanation for these trends, then you can stop reading now."

    There is. The increase in inequality, which has a very tight correlation ith the time series you just printed.

    What happened was that the poor and lower middle class got poorer, and were *unable* to save as much money as they did before. Meanwhile the rich were getting richer, and therefore did not think they *needed* to save money (they still had as much savings as they had before, why increase the rate of savings?) -- so they didn't make up for it.

    In other words, I think the savings rate change is due to the change in the distribution of income and wealth. Almost entirely.

    Your main point in this piece is well taken. Economists have avoided studying distributional issues *too*, when distributional issues are starting to be implicated in almost every economic issue there is. This is not so much the streetlight issue as the political-bias issue, but it is a case of not looking at the important problems, but at the "easy" problems.

    --Nathanael Nerode

  9. Simon,

    bjd has it. The taking on of debt delays saving. I say "delays" rather than "inhibits", because as you know the paying off of debt IS saving. People take on debt as a way of deferring saving. Or bringing forward consumption. It's the same thing.

    The question is WHY people were choosing to defer saving (bring forward consumption) for such a long time, and why that preference suddenly reversed in the financial crisis. I suspect the explanation is more psychological than anything.


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