[1] Tilburg Univ, Dept Econ, CentER, European Banking Ctr, NL-5000 LE Tilburg, Netherlands
[2] Univ Oxford, Ctr Study African Econ, Dept Econ, Oxford OX1 3UQ, England
[3] Univ Oxford, Oxford Ctr Anal Resource Rich Econ, Dept Econ, NL-5000 LE Tilburg, Netherlands