Explaining theories to Mom

More methodology-blogging...

Paul Krugman makes an interesting argument about clarity vs. abstruseness in academia: 

In my field there is indeed a problem with abstruseness, with the many academics who never even try to put their thoughts in plain language...[The problem is] not that laypeople don’t understand what the academics are saying. It is, instead, that the academics themselves don’t understand what they’re saying. 

Don’t get me wrong: I like mathematical modeling. Mathematical modeling is a friend of mine. Math can be a powerful clarifying tool... 

But it’s really important to step away from the math and drop the jargon every once in a while, and not just as a public service. Trying to explain what you’re doing intuitively isn’t just for the proles; it’s an important way to check on yourself, to be sure that your story is at least halfway plausible... 

I once talked to a theorist...who said that his criterion for serious economics was stuff that you can’t explain to your mother. I would say that if you can’t explain it to your mother, or at least to your non-economist friends, there’s a good chance that you yourself don’t really know what you’re doing. 

Math is good. Sometimes jargon is good, too. But plain language and simple intuition are important to keep you grounded.

My first reaction to this was "No way." Think of something like quantum mechanics. You can try to explain that to your mother, and it's going to go something like this: "Look, mom, an electron is both a particle and a wave. The wave sort of represents where you might think you found a particle. But after you find a particle, the wave instantly collapses and then starts expanding out again."

Got that?

Well, that explanation sounds simple, but it won't help Mom judge whether quantum mechanics is a good model or not, or understand anything about how it could be used. In fact, nobody really understands quantum mechanics, but we use it because it works. We tolerate the abstruseness of physics papers because that abstruseness is necessary to get a model that gives good quantitative predictions. In math, we tolerate abstruseness too - if you think quantum mechanics is hard, think of trying to explain number theory to your mom - because it "works" in the ways we want it to work.

There are branches of econ that work this way too. Explaining a Vickrey auction to your mom, or a random-utility discrete choice model, could possibly be very tough (depending on the mom), but there's no denying that these theories are extremely useful in their most technical forms, so we don't worry too much about their abstruseness. This is probably what Albert Einstein meant when he (allegedly) said: "Everything should be made as simple as possible, but no simpler."

What Krugman is implicitly arguing is that macroeconomics is different. The idea seems to be that since academic macro theory is not (yet) good for making quantitative predictions, we should focus more on communicating ideas. Communicating ideas - or "storytelling", as some call it - requires simplicity and clarity. Actually, that idea would not be too different from things Steve Williamson has said:

The problem is that any macroeconomic model is going to be wrong on some dimensions. To be useful, a model must be simple, and simplification makes it wrong in some sense. Subjected to standard econometric tests, it will be rejected. Models that are rejected by the data can nevertheless be extremely useful. I think that point is now widely recognized, and you won't find strong objections to it, as you might have in 1982.

Storytelling - communicating an idea about one mechanism that might be at work in the economy - is a far more modest goal than quantitative prediction. But that doesn't mean it's worthless.

I think the thing that Krugman is complaining about - and that Williamson would probably have less of a problem with - is models that lie somewhere between the intuitive and the quantitatively predictive. In a lot of DSGE-type models, you put in your assumptions, crank them through a set of generally accepted techniques, and come out with an intelligible story...but the intuition for how the machinery produces that story is not always clear or simple. 

On one hand, there seems to be no obvious reason why we should avoid making this kind of model, if we have enough time to poke it, play with it, and explore more about how it's getting the results it gets. But if we have to communicate our ideas very quickly, then models this complex can become more of a hindrance than a help. Some people who work for central banks have mentioned to me that in 2008-9, the unwieldiness of their modern DSGE-type macro models made it hard to communicate out-of-the-box thinking and unconventional policy suggestions. In that type of crisis situation, your colleague may be no better equipped to understand you than Mom.


Updates

Some more quotes from popular old physics types:

"You know, I couldn't do it. I couldn't reduce it to the freshman level. That means we really don't understand it."
- Feynman

"Hell, if I could explain it to the average person, it wouldn't have been worth the Nobel prize."
- Feynman

"You do not really understand something unless you can explain it to your grandmother."
- Einstein

"Never express yourself more clearly than you are able to think."
- Bohr