1. Princess Norah Bint Abdulrahman University; Riyadh 11635 Saudi Arabia
2. Statistics Department; Federal University of Bahia; Salvador Bahia 40170-110 Brazil
3. School of Mathematics & Statistics; Newcastle University; Newcastle upon Tyne NE1 7RU UK
4. Institute for Biostatistics and Medical Informatics; Faculty of Medicine; University of Ljubljana; Ljubljana 1000 Slovenia