If you're a fan of Monty Python and the Holy Grail, you'll know how. Since a witch burns, she must be made of wood, and since wood floats and ducks also float, logically a witch will weigh the same as a duck (or something like that). And if you have no idea what I'm talking about, this video clip from the absurd 1975 film should clear it up:
While witchcraft might seem to be the stuff of medieval legend, it is actually a tricky sociological - and, as it turns out, economic - question in some developing countries. Last week Raymond Fisman, a rising star at Colombia Business School, came to the World Bank to speak about his new book Economic Gangsters (coauthored with Edward Miguel). One of the stories from the book that Fisman related concerned witch killing, which is apparently not an uncommon phenomenon in some countries, Tanzania in particular.
Fisman is quite soft-spoken, so it was a bit jarring to hear him talk about how families will sometimes accuse an elderly female member of witchcraft and brutally murder her. As it turns out, there is an underlying economic logic to the practice of witch killing, and soft-spoken Fisman is just the person to explain it.
I will probably not do justice to his explanation, but here goes. When a family is hit by serious economic stress such as a drought, the members of the family have two choices. One option is to reduce each family member's consumption. However, if a family was living at the subsistence level before the economic stress began, then each person will starve. So the second option is to expel or murder one of the members of the family. And the person that tends to be picked is the one for whom the gap between consumption and production is the largest - in other words, the elderly. (There is undoubtedly a cultural influence about who gets picked as well - elderly men vs. elderly women or children vs. the elderly; however, the economic logic remains.)
And just as the rationale behind witch killing has roots in economic incentives, so does the solution. One possibility is to provide elderly women with pensions. In fact this is the solution Fisman's coauthor Edward Miguel suggests in a 2005 paper in the Review of Economic Studies on Poverty and Witch Killing (link is to an ungated 2004 draft version of the paper):
Another potentially attractive policy option is to provide elderly women in the study area with regular pensions, which would transform them from a net household economic liability into an asset, and could help households smooth their consumption. The South African case provides suggestive evidence that this could have a substantial impact: witch killings in Northern Province, South Africa have dropped dramatically since the introduction of an old age pension in the early 1990s (Singer 2000) – although it is, of course, difficult to definitively establish causality given the many other political and social changes that have occurred in South Africa during the same period.
I followed up with Fisman via email after the presentation to ask him about this issue. Fisman pointed out to me that although pensions in South Africa did have the beneficial side effect of reducing witch killings in South Africa, pensions are probably not the most effective way to deal with community-wide shocks like drought. I followed up: Would microinsurance be a better option? I didn't get a direct answer to this follow-on question, but Fisman did direct me to pages 148-155 of Economic Gangsters. Clearly, he understands incentives - Economic Gangsters is now at the top of my reading list.
Note: Many thanks to Fisman for graciously answering numerous of my emails.