1. a Department of Mathematics , K.U. Leuven , Celestijnenlaan 200B, 3001 Heverlee, Belgium
2. b Department of Statistics and Actuarial Science , University of Stellenbosch , Private Bag X1, Matieland 7602, South Africa
3. c Department of Applied Economics , K.U. Leuven, Naamsestraat 69, 3000 Leuven and University Centre for Statistics , K.U. Leuven, de Croylaan 54, 3001 Heverlee, Belgium