| Peter Klein |
This item in Tuesday’s W$J, “Is an Economist Qualified To Solve Puzzle of Autism?”, is required reading for those interested in the scope and methods of modern empirical economics. The piece focuses on Michael Waldman’s paper (with Sean Nicholson Nodir Adilov) linking autism to television, a link vehemently denied by other autism researchers and advocacy groups. More generally,
Prof. Waldman’s willingness to hazard an opinion on a delicate matter of science reflects the growing ambition of economists — and also their growing hubris, in the view of critics. Academic economists are increasingly venturing beyond their traditional stomping ground, a wanderlust that has produced some powerful results but also has raised concerns about whether they’re sometimes going too far.
Ami Klin, director of the autism program at the Yale Child Study Center, says Prof. Waldman needlessly wounded families by advertising an unpublished paper that lacks support from clinical studies of actual children. “Whenever there is a fad in autism, what people unfortunately fail to see is how parents suffer,” says Dr. Klin. “The moment you start to use economics to study the cause of autism, I think you’ve crossed a boundary.”
Moreover — how unusual is this for a newspaper story — there’s also an extended discussion of instrumental-variables estimation.
Waldman’s paper uses precipitation levels as an instrument for time watching TV to address the potential for reverse causality. Rainfall is exogenous, so while kids genetically predisposed toward autistic behavior may tend to watch more TV, they aren’t more likely to live in Seattle or Portland. If there is more autism in rainy places than dry places, it is likely that the additional time spent indoors — presumably in front of the tube — is at least one of the causes. Notes the WSJ reporter:
Such debates are likely to grow as economists delve into issues in education, politics, history and even epidemiology. Prof. Waldman’s use of precipitation illustrates one of the tools that has emboldened them: the instrumental variable, a statistical method that, by introducing some random or natural influence, helps economists sort out questions of cause and effect. Using the technique, they can create “natural experiments” that seek to approximate the rigor of randomized trials — the traditional gold standard of medical research.
Instrumental variables have helped prominent researchers shed light on sensitive topics. Joshua Angrist of the Massachusetts Institute of Technology has studied the cost of war, the University of Chicago’s Steven Levitt has examined the effect of adding police on crime, and Harvard’s Caroline Hoxby has studied school performance. Their work has played an important role in public-policy debates.
The article concludes with a detailed discussion of some of these studies, along with a helpful summary table which I’ve reproduced below.
It’s all very interesting. But what would Steve Sailer say?
Examples of instrumental-variables research in economics:
|Author(s)||Year*||Instrument||How it worked||Conclusion||Link|
|Joshua Angrist||1990||Vietnam draft lottery||Randomly made some people more likely to serve in the military than others||Being drafted into the Vietnam-era military reduced future earnings for white males||N.A.|
|Joshua Angrist and Alan Krueger||1991||Season of a student’s birth||Compulsory education laws forced people with later birthdates to stay in high school longer||Extra time in high school positively affected future earnings||N.A.|
|Steven Levitt||1997||Election cycles||Politicians tend to hire more police before election day||Additional police reduce violent crime||Read the paper8|
|Caroline Hoxby||2000||Number of streams in metropolitan areas||Led some metropolitan areas to have more school districts than others||Greater competition among school disctricts leads to better academic results||Read the paper9|
|Lakshmi Iyer||2004||Deaths of heirless rulers of Indian regions||Made region more likely to fall under British rule||Colonial administrators did a poorer job of providing public goods, such as schools and medical care, than did local rulers||Read the paper10|
|James Feyrer and Bruce Sacerdote||2006||Wind patterns||Blew European colonizers’ ships to some islands earlier than to others||Earlier colonization had a positive effect on islands’ future wealth||Read the paper11|
|Emily Oster||2006||Distance from the origin of the HIV virus in Africa||Caused some Africans to confront the HIV virus earlier than others||Wealthier Africans, and in general those who have reason to expect long lives, have cut back on risky sex in response to HIV||Read the paper12|
|Morten Bennedsen, Kasper Meisner Nielsen, Francisco Pérez-González and Daniel Wolfenzon||2006||Gender of CEO’s first-born child, among Danish firms||The presence of a first-born son makes the management of a family firm more likely to stay within the family||Nepotism harms firms’ profitability||Read the paper13|
|Ben Olken||2006||Signal strength in Indonesia||People with better reception watch more TV and listen to more radio||TV and radio have had a negative effect on social capital in Indonesia||Read the paper14|
*Initial publication or working paper