Applied Statistics


My colleague Macartan Humphreys recently came out with book, Coethnicity (with James Habyarimana, Daniel Posner, and Jeremy Weinstein, addresses the question of why public services and civic cooperation tend to be worse in areas with more ethnic variation. To put it another way: people in homogeneous areas work well together, whereas in areas of ethnic diversity, there’s a lot less cooperation.

From one perspective, this one falls into the “duh” category. Of course, we cooperate with people who are more like us! But it’s not so simple. Macartan and his colleagues discuss and discard a number of reasonable-sounding explanations before getting to their conclusion, which is that people of the same ethnic group are more able to enforce reciprocity and thus are more motivated to cooperate with each other.

But, looking at it another way, I wonder whether it’s actually true that people in homogenous societies cooperate more. I think of the U.S. is pretty ethnically diverse, compared to a lot of much more disorganized places. One question is what counts as ethnicity. Fifty or a hundred years ago in the U.S., I think we’d be talking about Irish, English, Italians, etc., as different ethnic groups, but now they’d pretty much all count as white. To what extent is noncooperation not just the product of ethnic diversity but also a contributor to its continuation?

Macartan and his collaborators address some of these issues in their concluding chapter, and I’m sure there’s a lot more about this in the literature. This is an area of political science that I know almost nothing about. When a researcher such as myself writes a book in American politics, we don’t have to explain much–our readers are already familiar with the key ideas. Comparative politics, though, is a mystery to the general reader such as myself.

I should say something about the methods used by Macartan and his collaborators. They went to a city in Uganda, told people about their study, and performed little psychology/economics experiments on a bunch of volunteers. Each experiment involved some task or choice involving cooperation or the distribution of resources, and they examined the results by comparing people, and pairs of people, by ethnicity, to see where and how people of the same or different ethnic groups worked together in different ways.

One thing that was cool about this study, and which reminded me of research I’ve seen in experimental psychology, was that they did lots of little experiments to tie up loose ends and to address possible loopholes. Just for example, see the discussion on pages 137-139 of how they rule out the possibility that their findings could be explained by collusion among study participants.

I was also thinking about the implications of their findings for U.S. politics. (Macartan has told me that he doesn’t understand how there can be a whole subfield of political scientist specializing in American politics, but he told me that he’ll accept “Americanists” by thinking of us as comparative politics scholars who happen to be extremely limited in what we study.) The authors allude to research by Robert Putnam and others comparing civic behavior in U.S. communities of varying ethnic homogeneity, but I also wonder about public opinion at the national level, not just local cooperation but also to what extent people feel that “we’re all in this together” and to what extent people evaluate policies and candidates based on how they effect their ethnic group (however defined). I’m also interested in the sometimes-vague links between ethnicity and geography, for example the idea that being a Southerner (in the U.S.) or a Northerner (in England) seems like an ethnic identity. Even within a city, different neighborhoods have different identities.

If I haven’t made the point clear enough already, I think the book is fascinating, and it looks like it will open the door to all sorts of interesting new work as well.


  1. #1 Vinny Burgoo
    January 3, 2010

    The text is posted twice.

  2. #2 Andrew Gelman
    January 4, 2010

    D’oh! Fixed.

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