David R. Henderson  

Krugman on Scientific Method

Prosecutorial Persecution... When to Trust Your Superiors...

Some of Paul Krugman's best posts are on scientific method, specifically, how do you judge a theory. One of his posts today is beautiful, or, more correctly, would have been beautiful had he dropped the last line. In that line, he attacks people who disagree with him politically. I'll quote, though, from the good part:

[James] Hutton was, for a time, a farmer -- and in that occupation, observing the process of erosion and the laying down of deposits of various materials, he realized that the landscape he saw around him could be explained by the same forces operating over immense periods of time, as long as you posited that there were other forces uplifting ancient sediments to form today's geological features. How could he know whether this theory was right? He made predictions; in particular, that in places you would find "angular uncomformities", striated bodies of sedimentary rocks from different eras that were tilted relative to each other.

Why do I like this story so much? I think because it's science of a kind everyone should be able to understand; it doesn't rely on exotic instruments or hard math (not that there's anything wrong with either of these), it just relies on keen observation and an open mind.

Unlike many people who comment on this blog, I do not hate Paul Krugman. I don't even dislike him. I could psychologize here about what I think drives Paul Krugman, but I think the ground rules for this blog push me not to.

But one positive thing that I think drives him, and it's apparent in the post I'm discussing, is a genuine interest and curiosity. The problem is that when he is so vitriolic at people he disagrees with, it's harder for him to run with that curiosity. The reason: every once in a while he will find that the views of someone he attacked for having those views are correct. Then he's in a bind: to admit that would mean he would have to disown some of his attacks. Ceteris paribus, it's harder to back down when you've been nasty.

I remember, when I was 18 and was a fan of Ayn Rand (I still am, but much more critically), Ellen Moore, a woman who headed the local Objectivist group in Winnipeg (they weren't supposed to call themselves "Objectivists," but "students of Objectivism") came by the University of Winnipeg and ran into my friend and mentor, Clancy Smith. Clancy invited Ellen to sit with him and the friend he was with. Ellen sat down and said hi. Clancy then introduced her to his friend and told her that his friend was a socialist. Well!

Ellen then asked him, prosecutor style, "Do you think the government has a right to take people's property?" "I'd never thought about it exactly that way, but, I guess, yes," answered the young man.

With that, Ellen got up and said, "I must leave. To sit here further and be polite would be to sanction your anti-life thoughts." (I'm recalling as best I can from the story Clancy told me 44 years ago, but it was something like that.)

Then she left. About a minute later, she returned, looking kind of sheepish. She explained that she had forgotten her gloves.

BTW, note what site Krugman links to in mentioning David Hume's contributions to economics.

Comments and Sharing

COMMENTS (29 to date)
Daniel Kuehn writes:

I think vitriol is largely in the eye of the beholder. I don't think Krugman is any worse on this count than say Boettke or Horwitz at Coordination Problem or Russ at Cafe Hayek, John Taylor, or Arnold's old posts here.

Don Boudreaux and Stephen Williamson kick it up a notch on the abrasiveness from Krugman IMO, as does DeLong on the other side.

I don't think Krugman's a particularly notable case on this. Krugman does call out Republican and libertarian politicians specifically and he does not call out Democrats as much. This is understandable - he thinks they're right! Libertarian blogs will call out Democrats and Republicans both a lot more than they'll call out libertarians.

genauer writes:

I do not think that Krugman understands science.

I ask this question:

Tell me one specific Krugman paper, and a few specific sentences, what YOU think is good about that paper.

Bostonian writes:

Is the Ellen in Henderson's story crazy? If so, I may be too, because I have similar thoughts.

A mugger is evil. Someone who believes that the government should have the right to confiscate any amount of a person's income to pay for welfare (including Social Security and Medicare) is in my view a mugger-by-proxy. Many Democrats do seem to believe that the government has this power. Previous Democratic presidents did raise the top income tax rate to 91%.

There are people who are Democrats for reasons I understand, such as not wanting rape victims to be forced to carry resulting pregnancies to term. But someone who seeks to do evil things through the political process deserves to be shunned.

Bob Murphy writes:


I don't have a problem with anything you said in this post, but something to think about: Do you think what Krugman is viewing as the scientific method is the right approach for understanding economic laws? I don't think it is. If the government raised the minimum wage and unemployment went down, I sure wouldn't change my views; I would assume other things weren't equal.

The way I piece it together, living organizations (including humans) need to make decisions in order to survive. But we living organizations can never gather all information. We have to develop strategies through which we can make good-enough decisions with a limited budget of information.

This necessarily entails turning away from choice-prospects. Even though a given choice-prospect might still have some promise to do good for us, we need to choose -- our best choice-prospects -- and move on. We have to reject some choices.

I suppose it is best if we do not go around crippled by guilt, guilt that we might feel about choices we have rejected. We need ways to keep our psyches comfortable with the rejections we've made.

As you can see, I'm building up to justifying the human mechanism of stereotyping other classes of people. Paul Krugman may be pre-forgiven. Do you think I can get there?

john hare writes:

I am a fan of Ayn Rand myself. I think refusing to interact with people of other viewpoints simply leaves the field to them. Leaving after some discussion would be different than running away and has some potential of bringing them to your point of view. The concept of not giving even moral support to bad actors is valid, but it sounds like the socialist in this case might not have been fixed in that viewpoint and might have had some hope of correction.

TomC writes:

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c141nav writes:

RE: I could psychologize here about what I think drives Paul Krugman...

I believe the answer is found in Jonathan Haidt's excellent book: The Righteous Mind

I am so glad that Arnold recommended this book back in March of this year

David R. Henderson writes:

@Bob Murphy,
I don't have a problem with anything you said in this post, but something to think about: Do you think what Krugman is viewing as the scientific method is the right approach for understanding economic laws? I don't think it is. If the government raised the minimum wage and unemployment went down, I sure wouldn't change my views; I would assume other things weren't equal.
I know this sounds wishy-washy, but I'm somewhere in between Milton Friedman and Ludwig von Mises on methodology. In your minimum wage case, I would bet, though not assume, that other things weren't equal or that the minimum wage was not binding.
Is the Ellen in Henderson's story crazy? If so, I may be too, because I have similar thoughts.
No, I don't think she was crazy. If you've read much of my colleague Bryan Caplan's work on mental illness, you'll know why.
I do think she was wrong. She was talking to a young man who, one could tell by the way he said it, wasn't totally sure of his views and probably hadn't been confronted about them the way she did. I think she came on too strong but, once having done so, should have stuck around. She wasn't wrong in a moral sense; rather, she was ineffective. If she didn't care about changing people's minds, then that's fine. But, and I know this because I knew her in other contexts, she cared passionately about changing people's minds.

David R. Henderson writes:

@john hare,
Whoops. I just saw your comment. Well said.

Steve Sailer writes:

Back in the 1990s, Krugman read up on evolutionary theory and came up with some good insights, especially into how Stephen Jay Gould was overrated:

SYNOPSIS: A look at a way to get beyond traditional Profit-Maximization theory into something more realistic.

(A talk given to the European Association for Evolutionary Political Economy)


Chris H writes:

Bostonian writes:

A mugger is evil. Someone who believes that the government should have the right to confiscate any amount of a person's income to pay for welfare (including Social Security and Medicare) is in my view a mugger-by-proxy.

There is one key difference here. A mugger has sole control over the decision whether to rob or not (excepting extraordinary circumstances like being coerced to mug someone, but that simply places blame one place back). In contrast the beliefs of any given regular socialist have no difference on the amount of mugging a government does. If that socialist changed his mind and voted differently that would not change any outcome. Even if he began advocating for a different cause and influenced 100 people to switch sides the chances of him actually having an impact on electoral outcomes, much less government actions, is effectively nil.

Under such circumstances the socialist (or any political partisan) is unlikely to form beliefs on a rational basis. On the other hand, a mugger has control over whether he will mug someone. If he undertakes a mugging it is with knowing that his beliefs on the rightness of mugging will impact whether the deed is done. He thus has no excuse not to engage in rational thought on the morality of his belief.

Under these circumstances, associating with a socialist is far less objectionable than associating with a mugger. You may want to watch out if you have any friends who've joined the IRS or DEA though.

David R. Henderson writes:

Tell me one specific Krugman paper, and a few specific sentences, what YOU think is good about that paper.
I already have, here and here.

rapscallion writes:

Far cheaper even than "profiling" per se, which can require extensive investigations, is too simply not serve suspect demographics whatsoever. I wouldn't be surprise if a completely free market in air travel gave rise to firms that simply didn't serve people with Arab backgrounds.

Seth writes:

At least Ellen provided rationale for the young man to ponder why she believed it wrong for the government to take property. I've learned a lot from folks yelling at me and foaming at their mouths.

I cannot say the same for Paul Krugman's post. Too many times have I seen correct predictions made on keen observation, but later the relation between the prediction and outcome was shone to be random.

A truly open mind doesn't stop when his prediction is correct. He'd be open to the idea that he might have been lucky.

A truly open mind also wouldn't shy away from admitting his opponents are right about something, even if he was a jerk to them.

Russ Roberts writes:

Daniel Kuehn,

You claim that Paul Krugman's vitriol level is no different from John Taylor's. As I wrote at Cafe Hayek about a year ago:

I did find a post where Krugman conceded that John Taylor “actually has a pretty good point.” That point is that there was actually very little stimulus in the 2009 stimulus package. Krugman calls that point “pretty good” either because he really thinks it is or because it confirms his own world view. The evidence suggests the latter. In other posts on Taylor he refers to a “zombie claim” of Taylor’s or says Taylor has lost his mind or that his mind is corroded, that it’s a “good bet he [Taylor] doesn’t believe what he’s saying.” I mention Taylor because I know him a little bit. He’s a fine person and thoughtful and I’ve never seen him write or say anything like this about his intellectual opponents.

If you can find some examples from John Taylor's blog, that are equally disrespectful, I'd sure like to see them. I mentioned John Taylor in that post because I knew Krugman had written about him a few times and those references were easy to find.

Krugman routinely says disrespectful things about people who disagree with him. I know John Taylor doesn't. I doubt the rest of the people on your list do either.

genauer writes:

@David Henderson
Thanks for your reply and links.
I am in agreement with you and PK that “sweatshop” jobs are better than their alternative, as long as there is no forced labor, otherwise people wouldn’t choose them, and that trade is in general good.

But I see this more as political statements and not “Science”.

I have asked now the question about PK scientific “papers” (here we do not use that term for popular books) in about 10 econ blogs, when it was related, and it seems that absolutely nobody has ever read any. At least not in a way, that she can describe the content in a kind of way of “this fact or insight was not known before” . Or some facts are for the first time explained quantitatively, with a coherent model. Something like that.

So I give it here a shy second try. People have repeatedly become offensive, when I insisted on something more specific.

Tom West writes:

I do not think that Krugman understands science.

I think Krugman *does* understand science. However, he has chosen the path of politics, and where the two conflict, politics wins. Like any good salesman, he uses every tool at his disposal, and that includes his reputation in economics.

I'm a little sad because I think the world would be better off with him as an economist rather than a salesman, but I'm not going to fault him. His career path would have been far less lucrative or interesting as simply a somewhat notable economist.

genauer writes:

I will get to the Krugman books, you mentioned, only tomorrow, we have a holiday here, bookstores closed and even the library! Saxony really wants to make sure that we dont get distracted from praying and repenting our sins : - )

Anyways, any more specific hint is here welcome as well.

2. Government taking our property

My understanding here is, that most people mean primarily taxes (on income) with that. Taxes exist as long as human societies with a written track, or ...
The question is just, how much is justified. And the 91% tax were not changed under GOP presidents as well, right?

I think in the early 2000's there was a Supreme Court decision on "eminent domain", taking area and shags away from people (in Boston?) to built a new mall. I do not recall much lamenting about that.

Bedarz Iliaci writes:

"it just relies on keen observation and an open mind."

Not too open. In fact, scientists tend to be very stubborn in holding on to their pet theories. And it is this very stubbornness and frankly close-mindedness that drives them to explore their pet theories and ferret out possible objections and situations where the theory could be tested.
One must love something in order to know it. Thus too much of open-mindedness hinders the single-mindedness that is essential to the scientist.
See for example, Authur Koestler's The Sleepwalkers for the detailed description of how Copernicus, Kepler and Galileo labored and made their discoveries. They were not open-minded but pursued their vision fanatically.

genauer writes:

Tom West

A specific paper? Please?

I did not start this with “lets pick on Krugman, because I don’t like most of what he says”. On the contrary, I was pretty sympathetic to him, some time ago. I am pretty interested in a lot of topics, he is linked to: international trade, geography of economics, exchange rates. Coming from physics, I love equations : - ) I even have financial beef in this.

I wanted to learn something from his papers, and I read them, and then I was always at a loss. I am asking so penetrating, to be sure I didn’t miss anything, and second to check on my increasing fear, that what people in economics consider “science” is very different from what I am used to.

David R. Henderson writes:

I am in agreement with you and PK that “sweatshop” jobs are better than their alternative, as long as there is no forced labor, otherwise people wouldn’t choose them, and that trade is in general good.

But I see this more as political statements and not “Science."

No, they're actually economics, not political statements. It's just that they're reasoned so clearly that they seem simple. That can lead people to think that they're not reading economics. But they are.

But I take your point. I'm not as familiar with his academic work as I should be. I liked his dissertation but it's been a long time since I read the article he pulled out of it. If I recall, it was on applying monopolistic competition to international trade.

genauer writes:

@David Henderson

Thanks for your thorough reply.

1. I am very aware that the situation is a little bizarre. Some nobody comes and says, I don’t see any value in a Nobel prize winner, who is a demi god for some folks.

2. I don’t want to hassle anybody or get on the nerves

3. I still hope that somebody shows me the nuggets of wisdom in Krugmans work, but I don’t see them so far

I have the J. Intern. Econ. 9(1979)469 -479 “Increasing Returns, Monopolistic Competition, and International Trade” in front of me. I think that is what you mentioned. We could also talk 1978 Purchasing power parity, or 1979 A model of innovation …….

He dutifully names the usual known names Balassa, Ohlin … : -)

He makes an unusual assumption about labor / output relation. Some additional assumptions, no unemployment, …. O.k.,

same wages ??, no differences in productivity, zero transport costs, balanced trade, same tastes, perfect labor mobility, all well known not exactly true, then plays a little with some sums, and then ….. what ?

“Factor mobility can substitute for trade” “labor will concentrate in a single region”

Is that it? A number of false assumptions leading to conclusions, which are obviously not true in reality?

Or what do I miss here?

I have already asked the same question Nick Rowe, Brad deLong, Scott Sumner, Noah Smith, Tyler Cowen, a couple of Irish econ professors.

We could take it offline, somebody else you could recommend to ask,or …. Whatever you propose.

I had already nearly given up, but your comment

“Some of Paul Krugman's best posts are on scientific method, specifically, how do you judge a theory. One of his posts today is beautiful, or, more correctly, would have been beautiful”

encouraged me to give it one more try.

I am relatively new to macro, physics background, but with a double digit h-index and close to 1000 citations I am confident that I can read and write papers.


Tom West writes:

genauer: I misunderstood. I thought by "science" you were referring to economics/math in general.

I can't say that I know his ability with science, but I find it rather likely that ability with the math behind high level economics bleeds into the other hard sciences.

I could be wrong, though.

Charlie writes:


If you want to understand Krugman's contributions to economics, the nobel prize committee has written extensively about it and provided links to further readings:


Reading your posts though, it seems that you question whether a simple model with unrealistic assumptions can provide useful insights. Alas, that is not something that can be explained in a few sentences. And there is no guarantee that even after the best made case, that it would change your mind.

If you are genuinely open minded though, you might consider Paul Krugman's own case for such work. He really does exemplify the "quantitative parable" brand economics. The idea that a simple, abstract story can provide insight. You might look at these essays.

How I work

Two Cheers for Formalism

Charlie writes:

Here is a nice bit from the first essay:

Simplify, simplify

The injunction to dare to be silly is not a license to be undisciplined. In fact, doing really innovative theory requires much more intellectual discipline than working in a well-established literature. What is really hard is to stay on course: since the terrain is unfamilar, it is all too easy to find yourself going around in circles. Somewhere or other Keynes wrote that "it is astonishing what foolish things a man thinking alone can come temporarily to believe". And it is also crucial to express your ideas in a way that other people, who have not spent the last few years wrestling with your problems and are not eager to spend the next few years wrestling with your answers, can understand without too much effort.

Fortunately, there is a strategy that does double duty: it both helps you keep control of your own insights, and makes those insights accessible to others. The strategy is: always try to express your ideas in the simplest possible model. The act of stripping down to this minimalist model will force you to get to the essence of what you are trying to say (and will also make obvious to you those situations in which you actually have nothing to say). And this minimalist model will then be easy to explain to other economists as well.

I have used the "minimum necessary model" approach over and over again: using a one-factor, one-industry model to explain the basic role of monopolistic competition in trade; assuming sector-specific labor rather than full Heckscher-Ohlin factor substitution to explain the effects of intraindustry trade; working with symmetric countries to assess the role of reciprocal dumping; and so on. In each case the effect has been to allow me to tackle a subject widely viewed as formidably difficult with what appears, at first sight, to be ridiculous simplicity.

The downside of this strategy is, of course, that many of your colleagues will tend to assume that an insight that can be expressed in a cute little model must be trivial and obvious -- it takes some sophistication to realize that simplicity may be the result of years of hard thinking. I have heard the story that when Joseph Stiglitz was being considered for tenure at Yale, one of his senior colleagues belittled his work, saying that it consisted mostly of little models rather than deep theorems. Another colleague then asked, "But couldn't you say the same about Paul Samuelson"? "Yes, I could", replied Joe's opponent. I have heard the same reaction to my own work. Luckily, there are enough sophisticated economists around that in the end intellectual justice is usually served. And there is a special delight in managing not only to boldly go where no economist has gone before, but to do so in a way that seems after the fact to be almost childs' play.

I have now described my basic rules for research. I have illustrated them with my experience in developing the "new trade theory" and with my more recent extension of that work to economic geography, because these are the core of my work. But I have also done quite a lot of other stuff, which (it seems to me) is also in some sense part of the same enterprise. So in the remainder of this essay I want to talk about this other work, and in particular about how the policy economist and the analytical economist can coexist in the same person.

Aaronson writes:

Vitriol? Surely not. "I’ve never gone ad hominem on them."

No wonder you don't dislike him. Who could dislike such a wonderful (by his own admission) guy?

genauer writes:


I have asked
“Tell me one specific Krugman paper, and a few specific sentences, what YOU think is good about that paper.” For good reason in this way.

These general, unspecific hints at somebody else has said, Krugman did some good work in this or that field are available in abundance, including the nobel prize committee.

But if you try to look at what specifically, nobody can produce anything from Krugman.
Usual Krugman starts with some, often unrealistic assumptions, then plays a little bit with the equations, and his “result” is then always not comparable to some real world data, on principle, at least in what I have seen so far. But I wanted to be deliberately open minded in the formulation, to see, what others might find valuable in a specific piece of him.

The only one who ever tried to name a specific paper, was Noah Smith, http://noahpinionblog.blogspot.com/2012/10/reinhart-rogoff-vs-bordo-haubrich-with.html?showComment=1350684684318#c7879317277481749370
who claimed that the 1991 paper would explain city size distribution (Zipf’s law), which it didn’t not at all. The explanation Krugman copied in 1996 from somebody else (Simon 1955) has nothing to do with any economic variables. I don’t want to repeat here the detailed argument of the link.
Stating his intentions or hopes for outcome is not “results”.

Krugman doesn’t explain or predict anything, he doesn’t show evidence. He just plays with some abstract equations.

And this is not (economic) science, as I know it. (@ Tom West)

genauer writes:

Paul Krugman versus the truth – wiki edition

For the majority of you, who do not read “scientific” papers, please take a short look at what Krugman wrote, and how it really was, as you can find in the wiki of James Hutton, and links there.

Krugman’s story is that an individual Hutton observed the layered structure and composition of the layers, to make then the “prediction” of “angular unconformities”. And Wang, as soon as he finds them, he turns that one observation into a pivotal point of a full geological theory.

The typical Krugman hyper simplified one genius, one factor, one gigantic conclusion theme.

When you read the James Hutton wiki, a very different picture emerges. “angular unconformities” had already been observed a century earlier by some Nicolas Steno, Hutton was contemplating “various ideas” for many years, fossils found were well known before to be from ancient fish, granite as formerly molten material penetrating other layers, etc. The idea that these layers were formed in previous oceans was around long before (Steno). Hutton added the argument that this happens all the times, many times.
When a James Hutton was looking for “angular unconformities”, he did not want to discover them, he knew they existed, but because he wanted to inspect them for detailed evidence, “particular marks”, for which his first discovery at Lochranza was actually not good enough for him. He did not stumble about them by accidental “keen observation”, but because of, and after a quite lengthy, systematic search.

The real story emerging here is the typical one of science, and not only in hard natural science. Everybody is standing on the shoulders of those who already observed and investigated before him, you discuss and explore things with others, and the evidence is most the times not just one example of existence, but lots of various evidence, quantitative agreement between theory and evidence, and lots of details of the evidence, generated by systematic work, which then generate as a total a convincing case for one out of several theories in discussion.

In summary, it is the exact opposite of how Paul Krugman operates.

To repeat myself: I do not think that Krugman understands science. At least he doesn’t practice it.

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