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history, the stock market, and predicting the future

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So the stock market has been freaking out a bit the last couple of weeks. Secular stagnation, Ebola, a five-year bull market—who knows why. Anyway, over the weekend I was listening to someone on NPR explain what the average person should do under such circumstances (answer: hang tight, don’t try to time the market). This reminded me of one of my pet quibbles with financial advice, which I think applies to a lot of social science more generally.

For years, the conventional wisdom around what ordinary folks should do with their money has gone something like this. Save a lot. Put it in tax-favored retirement accounts. Invest it mostly in index funds—the S&P 500 is good. Don’t mess with it. In the long run this is likely to net you a reliable 7% return after inflation, about the best you’re likely to do.

Now, it’s not that I think this is bad advice. In fact, this is pretty much exactly what I do, with some small tweaks.

But it has always struck me how, in news stories and advice columns and talk shows, people talk about how this is a good strategy because it’s worked for SO LONG. For 30 years! Or since 1929! Or since 1900! (Adjust returns accordingly.)

And yes, 30 years, or 85, or 114, are all a long time relative to human life. And we have to make decisions based on the knowledge we’ve got.

But it’s always seemed to me that if what you’re interested in is what will happen over the 30+ years of someone’s earning life (more if you’re not in academia!), you’ve basically got an N of 1 to 4 here. I mean, sure, this may be a reasonable guess, but I don’t think there’s any strong reason to believe that the next 100 years are likely to look very similar to the last 100. Odds are better if you’re just interested in the next 30, but even then, I’m always surprised by just how confident the conventional wisdom is around the idea that the market always coming out ahead over a 25- or 30-year period—going ALL THE WAY BACK TO 1929—is rock solid evidence that it will do so in the future.

Of course, there are lots of people who don’t believe this, too, as evidenced by what happened to gold prices after the financial crisis. Or by, you know, survivalists.

Anyway, I think this overconfidence in the lessons of the recent past is something we as social scientists tend to be susceptible to. The study that comes most immediately to mind here is the Raj Chetty study on value-added estimates of teachers (paper 1, paper 2, NYT article).

The gist of the argument is that teachers’ effects on student test scores, net of student characteristics (their value added), predicts students’ eventual income at age 28. Now, there’s a lot that could be discussed about this study (latest round of critique, media coverage thereof).

But I just want to point to it—or rather, broader interpretations of it—as illustrating a similar overconfidence in the ability of the past to predict the future.

Here we have a study based on a massive (2.5 million students) dataset over a twenty-year period (1989-2009). Just thinking about the scale of the study and taking its results at face value, it’s hard to imagine how much more certain one could be in social science than at the end of such an endeavor.

And much of the media coverage takes that certainty and projects it into the future (see the NYT article again). If you replace a low value-added teacher with an average one, the classroom’s lifetime earnings will increase by more than $250,000.

And yet to make such a leap, you have to be willing to assume so many things about the future will be like the past: not only that incentivizing teachers differently and making tests more important won’t change their predictive effects (which the papers acknowledge), but, just as importantly, that the effects of education on earnings—or, more specifically, of teacher value-added on earnings—will be similar in future 20-year periods as it was from 1989-2009. And that nothing else meaningful about teachers, students, schools, or earnings will evolve over the next 20 years in ways that mess with that relationship in a significant way.

I think we do this a lot—project into the future based on our understanding of a past that is, really, quite recent. Of course knowledge about the (relatively) recent past still should inform the decisions we make about the future. But rather a lot of modesty is called for when making blanket claims that assume the future is going to look just like the past. Maybe it’s human nature. But I think that modesty is often missing.

Written by epopp

October 20, 2014 at 11:01 am

if sociology had an igm panel

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The IGM panel of economic experts got some recent buzz because 63% of their experts — 81%, when weighted by confidence — disagree with the Piketty-inspired argument that r > g is driving recent wealth inequality in the U.S.

I always enjoy reading these surveys. The panel includes 50 or so top academic economists, from a variety of subfields and political orientations, and asks them whether they agree or disagree with a policy-relevant economic statement. Respondents answer on a Likert scale, and indicate their degree of certainty as well as their level of agreement. Sometimes they add a short comment.

The results usually aren’t incredibly surprising. Not really shocking that 100% of economists agree that

Letting car services such as Uber or Lyft compete with taxi firms on equal footing regarding genuine safety and insurance requirements, but without restrictions on prices or routes, raises consumer welfare.

They’re a little more nervous about selling kidneys (45% favor, but nearly 30% find themselves “uncertain” — the highest proportion for any recent question besides whether ending net neutrality is a good thing). The most interesting ones are those where there’s disagreement (Have the last decade of airline mergers improved things for travelers?) or that counter the stereotype (54% disagree that giving holiday presents — rather than cash — is inefficient. Okay, counters it a little).

Anyway, this got me wondering. What if sociology had a similar panel? I mean, aside from the fact that no one would care. I can think of empirical findings we’d have broad confidence in that much of the public wouldn’t buy — for example, that there’s lots of hiring discrimination against African-Americans. But are there policy prescriptions we’d agree on — ones that are grounded in the discipline, as opposed coming solely from our left-leaning tendencies, though of course the two are hard to separate — that would tell us, Yep, sociologists WOULD say that.

EDITED TO ADD: Yes, I know that Piketty does not actually argue r > g is the cause of recent inequality growth in the US, which is what the question asks. But if they can headline the poll “Piketty on Inequality,” it seems fair to call the statement “Piketty-inspired.”

Written by epopp

October 16, 2014 at 2:43 am

funk and hirschman on derivatives

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All around super nice guys and scholars Russell Funk and Dan Hirschman have a new paper in ASQ on financial regulations. The basic idea is that new securities can slowly unravel regulatory schemes:

Regulators, much like market actors, rely on categorical distinctions. Innovations that are ambiguous to regulatory categories but not to market actors present a problem for regulators and an opportunity for innovative firms. Using a wide range of primary and secondary, qualitative and quantitative sources, we trace the history of one class of innovative financial derivatives—interest rate and foreign exchange swaps—to show how these instruments undermined the separation of commercial and investment banking established by the Glass–Steagall Act of 1933 even as overt political action failed to do so. Swaps did not fit neatly into existing product categories—futures, securities, loans—and thus evaded regulatory scrutiny for many years. The market success of swaps put commercial and investment banks into direct competition and, in so doing, undermined Glass–Steagall. Drawing on this case, we theorize that ambiguous innovations may disrupt the regulatory status quo and shift the political burden onto parties that want to maintain existing regulations. Our findings also suggest that category-spanning innovations may be more valuable to market participants if regulators find them difficult to interpret.

Read the whole paper here.

50+ chapters of grad skool advice goodness: Grad Skool Rulz/From Black Power 

Written by fabiorojas

October 13, 2014 at 4:16 am

Posted in economics, fabio, markets

nussbaum on GDP alternatives

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Written by fabiorojas

October 4, 2014 at 12:01 am

if granovetter wins the nobel, remember that orgtheory called it back in 2007

Thomson Reuters has released a press announcement about their predictions for the 2014 Nobel prizes. They project it based on citation patterns. Check out the section on economics:

Mark S. Granovetter
Joan Butler Ford Professor and Chair of Sociology, and Joan Butler Ford Professor in the School of Humanities and Sciences, Stanford University
Stanford, CA USA

For his pioneering research in economic sociology

Kewl!!! Even if Granovetter never wins, he’ll always be recognized as a leader in sociological approaches to markets. And remember, if he does win – WE CALLED IT IN 2007. And yes, we just based it on citation patterns.

H/T: Umut Koc, who posted this on the Facebook orgtheory group.

50+ chapters of grad skool advice goodness: Grad Skool Rulz/From Black Power

Written by fabiorojas

October 1, 2014 at 12:01 am

Posted in economics, fabio, sociology

a whole pile of piketty

Econlog collects a few links:

Bon appetit.

50+ chapters of grad skool advice goodness: Grad Skool Rulz/From Black Power

 

Written by fabiorojas

September 26, 2014 at 12:02 am

gordon tullock and james buchanan on the calculus of consent

50+ chapters of grad skool advice goodness: Grad Skool Rulz/F

Written by fabiorojas

September 20, 2014 at 12:01 am

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