Sean Carroll on social science vs. natural science

I generally don't like to repost other people's blog posts in full on my blog, because it deprives the writers of pageviews. And of course the fact that I say that reliably indicates that I'm about to make an exception. Sean Carroll, who writes for the physics blog Cosmic Variance over at Discover, has written an absolute must-read post on social science vs. natural science. So here it is in full, with emphasis added by me:

Over on the Google+, Robin Hanson asks a leading question: 

Explain why people shouldn’t try to form their own physics opinions, but instead accept the judgements of expert physicists, but they should try to form their own opinions on economic policy, and not just accept expert opinion there. 

(I suspect the thing he wants me to explain is not something he thinks is actually true.) 

There are two aspects to this question, the hard part and the much-harder part. The hard part is the literal reading, comparing the levels of trust accorded to economists (and presumably also political scientists or sociologists) to the level accorded to physicists (and presumably also chemists or biologists). Why do we — or should we — accept the judgements of natural scientists more readily than those of social scientists? 

Although that’s not an easy question, the basic point is not difficult to figure out: in the public imagination, natural scientists have figured out a lot more reliable and non-obvious things about the world, compared to what non-experts would guess, than social scientists have. The insights of quantum mechanics and relativity are not things that most of us can even think sensibly about without quite a bit of background study. Social scientists, meanwhile, talk about things most people are relatively familiar with. The ratio of “things that have been discovered by this discipline” to “things I could have figured out for myself” just seems much larger in natural science than in social science. 

Then we stir in the matter of consensus. On the very basics of their fields (the Big Bang model, electromagnetism, natural selection), almost all natural scientists are in agreement. Social scientists seem to have trouble agreeing on the very foundations of their fields. If we cut taxes, will revenue go up or down? Does the death penalty deter crime or not? For many people, a lack of consensus gives them license to trust their own judgment as much as that of the experts. To put it another way: if we talked more about the bedrock principles of the field on which all experts agreed, and less about the contentious applications of detailed models to the real world, the public would likely be more ready to accept experts’ opinions. 

None of which is to say that social scientists are less capable or knowledgable about their fields than natural scientists. Their fields are much harder! Where “hard” characterizes the difficulty of coming up with models that accurately capture important features of reality. Physics is the easiest subject of all, which is why we know enormously more about it than any other science. The social sciences deal with fantastically more complicated subjects, about which it’s very naturally more difficult to make definitive statements, especially statements that represent counterintuitive discoveries. The esoteric knowledge that social scientists undoubtedly possess, therefore, doesn’t translate directly into actionable understanding of the world, in the same way that physicists are able to help get a spacecraft to the moon. 

There is a final point that is much trickier: political inclinations and other non-epistemic factors color our social-scientific judgments, for experts as well as for novices. On a liberal/conservative axis, most sociologists are to the left of most economists. (Training as an economist allegedly makes people more selfish, but there are complicated questions of causation there.) Or more basically, social scientists will often approach real-world problems from the point of view of their specific discipline, in contrast with a broader view that the non-expert might find more relevant. (Let’s say the death penalty does deter crime; is it still permissible on moral grounds?) Natural scientists are blissfully free from this source of bias, at least most of the time. Evolution would be the obvious counterexample. 

The more difficult question is much more interesting: when should, in completely general terms, a non-expert simply place trust in the judgment of an expert? I don’t have a very good answer to that one. 

I am a strong believer that good reasons, arguments, and evidence are what matter, not credentials. So the short answer to “when should we trust an expert simply because they are an expert?” is “never.” We should always ask for reasons before we place trust. Hannes Alfvén was a respected Nobel-prizewinning physicist; but his ideas about cosmology were completely loopy, and there was no reason for anyone to trust them. An interested outsider might verify that essentially no working cosmologists bought into his model. 

But a “good reason” might reasonably take the form “look, this is very complicated and would take pages of math to make explicit, but you see that I’ve been doing this for a long time and have the respect of my peer group, which has a long track record of being right about these issues, so I’m asking you to go along this time.” In the real world we don’t have anything like the time and resources to become experts in every interesting field, so some degree of trust is simply necessary. When deciding where to place that trust, we rely on a number of factors, mostly involving the track record of the group to which the purported expert belongs, if not the individual experts themselves. 

So my advice to economists who want more respect from the outside world would be: make it much more clear to the non-expert public that you have a reliable, agreed-upon set of non-obvious discoveries that your field has made about the world. People have tried to lay out such discoveries, of course — but upon closer inspection they don’t quite measure up to Newton’s Laws in terms of reliability and usefulness. 

Social scientists are just as smart and knowledgable as natural scientists, and certainly have a tougher job. But trust among non-experts isn’t demanded, and shouldn’t be based on credentials; it is given on the basis of a long track record of very visible success. Everyone would be in favor of that.

As far as I am concerned, every single thing written in this post is spot-on. I just have a few additional points:

1. What Carroll is saying is far more true of macroeconomics than microeconomics. Microeconomists are pretty good at predicting how bidders will bid at an auction, or how many people will use a new planned subway extension. (An old prof of mine once successfully managed to predict the relative amounts of denominations of money that counterfeiters would fake!) People don't often hear about these quiet successes, caught up as they are in the failures of macro. But they are real.

2. Although the lack of consensus among (macro)economists should give laypeople pause, the converse does not hold; the fact of consensus on a particular issue doesn't mean economists are right. The "Great Moderation" idea, for example, was as near to a business-cycle theory consensus as one could find, but collapsed in the wake of the recent crisis. As another example, a common defense of the DSGE modeling paradigm is that "everybody's doing it." Sorry, but no.

3. Carroll doesn't go into this, but the microfoundations of a discipline are also a factor in how much its experts should be trusted. Climatology has too long a horizon to make repeated verifiable predictions, but it's microfounded by physics that everyone agrees on. Macroeconomics, on the other hand, is microfounded on the parts of microeconomics that we don't really understand yet - consumption-saving behavior, firm investment decisions, technological change, expectation formation, risk aversion, and the like. Once micro people get these nailed down (and I think they will), we'll get some much more credible macro models.

Anyway, go check out the original link, which has some interesting links of its own.


Update: Robin Hanson responds to Carroll. The key argument is this:

Yes, economists were only a supporting influence in creating all those great economic institutions...But similarly, physicists were only a supporting influence in creating all those great physical devices...There were useful steam engines long before thermodynamics helped explain them, and it took far more than basic physics to get men to the moon, just as it took far more than basic economics to create modern industries. It is actually quite hard to say which discipline has been more useful overall to the world. 

This just seems wrong to me. You need to know Newton's Laws to hit the moon with a rocket. You don't need to know supply and demand curves to build a company. Physics theory has been absolutely essential to the creation of a number of industries, economics only to a couple, macroeconomics to basically none. And it should also be noted that before the mid-1900s, economics was non-quantitative, basically a type of philosophy. Which means that back when things like the corporation and the factory were being invented, economists' role was mainly as cheerleaders for free markets. Which was a very important role, but was a political role, not a scientific one.