Tuesday, 9 April 2013

Good experimental designs

Habyarimana, Humphreys, Posner and Weinstein wrote a great article with the title “Why Does EthnicDiversity Undermine Public Goods Provision?” which they turned into a great book Coethnicity. The research they report was a set of experiments in a slum of Kampala in Uganda.

The standard way experimentalists investigate public goods – say, schooling or sanitation – is with, guess what, a public goods game. A public goods game goes like this: there are four of you, and you each have, say, £10. You can each put some or all of your money into a common pot. Money in the pot is multiplied by 1.5 and then shared out equally. Selfish people wouldn't put money in the pot, but if everyone does so, then you all do better. This is a bare bones representation of a public good.  Why do experimenters use this paradigm? Well, it's obvious. We're interested in public goods, and a public goods game is like a miniature public good.

One of the surprising things about HHPW's design is this. They get their subjects to play dictator games (where one person chooses how much to give to another), games where they have to find another person in the slum, and experiments where they must work with other subjects to solve a puzzle. But they never actually implement a public goods game. Instead, they use a set of simple experiments, not in the context of public goods, to investigate specific psychological and social mechanisms that might lead to underprovision of public goods. For example, are people more altruistic to their coethnics? The Dictator Game will tell us. Or, do people find it easier to communicate with coethnics? Try the puzzle-solving activity.

I think this makes HHPW an example of good experimental research design. They have thought hard about the link between experiment and explanandum. Not that public goods games cannot be useful, but we should not just reach in our designs for things that “look like” or “represent” what we are investigating. Instead, the link must always be based in theory.