Thanks for the answers. Indeed, I wrote wrong in my examples the variables x and y I meant to say > y <- c(1,7,14,25,29,30) > x <- c(1,2,3,4,10,20) Thanks -- View this message in context: http://r.789695.n4.nabble.com/Fitting-my-data-to-a-Weibull-model-tp3780169p3781746.html Sent from the R help mailing list archive at Nabble.com.