Joao Santos Silva Department of Economics, University of Essex   Wivenhoe Park Colchester, CO4 3SQ United Kingdom   jmcss@essex.ac.uk   http://www.essex.ac.uk/economics/people/staff/jmcss.shtm       Primary Research Focus: Microeconometrics, Specification tests   JEL Areas: C1 : Econometric and Statistical Methods: General