Thanks for all the help. I also checked Dalgaard's R book and the explanation of the wilcox.test is very clear compared to the example in R documentation. Thanks. :handshake: -- View this message in context: http://old.nabble.com/wilcox.test-construction-in-r-tp26148779p26156041.html Sent from the R help mailing list archive at Nabble.com.