Anonymity and Indelity: Ethnic Identity, Strategic Cross-Ethnic Sexual Network Formation, and HIV/AIDS in Africa1

We develop a theory of how community-level ethnic heterogeneity determines the formation of sexual networks, and how this, in turn, a¤ects the spread of HIV/AIDS. Speci…cally, the model assumes that agents derive utility from sexual relationships, but sexual in…delity is prohibited and punished if detected by the cheated partner. We show that when information circulates more easily within ethnic groups than across, agents tend to choose their partners from di¤erent groups to hide their in…delity, due to cross-group anonymity. This optimizing behavior in turn implies a mechanism wherein ethnic heterogeneity encourages sexual in…delity and directly a¤ects the spread of HIV/AIDS. We use micro-level data from several sub-Saharan African countries to test these predictions of the model. In doing so, we …nd: (1) evidence for strategic cross-ethnic sexual interactions; and (2) a direct e¤ect of ethnic heterogeneity on both the number of sexual partners and HIV infection. Robustness checks show that this e¤ect is not driven by a lack of public goods in more ethnically diverse communities. Interestingly, ethnic heterogeneity is shown to have no e¤ect on anemia, which unlike HIV/AIDS, does not involve socially prohibited human interactions. This …nding supports our theory that diseases driven by socially prohibited human interactions spread through hidden and anonymous networks. Our study o¤ers a new explanation for the high concentration of the AIDS epidemic in sub-Saharan Africa. JEL Codes: A14, D71, I10, J10, O1. Keywords: Ethnic identity; ethnic heterogeneity; anonymity; in…delity; strategic sexual network formation; HIV/AIDS; Africa. 1 I am grateful to Andrew Foster for advice and guidance. My gratitude also goes to Charles Becker, Gervais Beninguisse, Francis Bloch, Ken Chay, Jakina Debnam, Esther Du‡o, Parfait Eloundou-Enyegue, Jane Fortson, Je¤rey Greenbaum, Rachel Heath, Leigh Johnson, Navin Kartik, Blessing Uchenna Mberu, Isaac Mbiti, Roger Myerson, Sriniketh Nagavarapu, Marie Patience Pongou, Sam Preston, Michelle Poulin, Louis Putterman, Paul Schultz, Roberto Serrano, Adam Storeygard, Olumide Taiwo, David Weil, and several participants at the Brown University Department of Economics Micro Lunch, the 2008 Northeast Universities Development Consortium at Boston University, the 64th European Meeting of the Econometric Society in Barcelona, and the 26th IUSSP International Population Conference in Marrakech for useful discussions and feedback. Anne Buvé and Linda Morison provided unique data from the Multicentre Study Group. The Department of Economics, the Graduate School, the Population Studies and Training Center and the Hewlett Packard Foundation provided generous …nancial support. 2Department of Economics, Brown University, 64 Waterman Street, Providence, RI 02912, U.S.A.; [email protected].