Hi, in the code below, I am drawing 1000 samples from two beta distributions, each time using the same random number seed.
Using set.seed(80) produces results I expect, in that the differences between the distributions are very small. Using set.seed(20) produces results I can't make sense of. Around half of the time, it behaves as with set.seed(80), but around half of the time, it behaves very differently, with a much wider distribution of differences between the two distributions. # Beta parameters #distribution 1 u1.a <- 285.14 u1.b <- 190.09 # distribution 2 u2.a <- 223.79 u2.b <- 189.11 #Good example: output is as expected set.seed(80); u1.good <- rbeta(1000, u1.a, u1.b) set.seed(80); u2.good <- rbeta(1000, u2.a, u2.b) #Bad example: output is different to expected set.seed(20); u1.bad <- rbeta(1000, u1.a, u1.b) set.seed(20); u2.bad <- rbeta(1000, u2.a, u2.b) # plot of distributions using set.seed(80), which behaves as expected plot(u2.good ~ u1.good, ylim=c(0.45, 0.70), xlim=c(0.45, 0.70)) abline(0,1) # plot of distributions using set.seed(20), which is different to expected plot(u2.bad ~ u1.bad, ylim=c(0.45, 0.70), xlim=c(0.45, 0.70)) abline(0,1) # plot of differences when using set.seed(80) plot(u1.good - u2.good, ylim=c(-0.2, 0.2)) abline(h=0) # plot of differences when using set.seed(20) plot(u1.bad - u2.bad, ylim=c(-0.2, 0.2)) abline(h=0) Could you explain why using set.seed(20) produces this chaotic pattern of behaviour? Many thanks, Jon -- Dr Jon Minton Research Associate Health Economics & Decision Science School of Health and Related Research University of Sheffield Times Higher Education University of the Year Tel: +44(0)114 222 0836 email: j.min...@sheffield.ac.uk http://www.shef.ac.uk/scharr/sections/heds http://scharrheds.blogspot.co.uk/ [[alternative HTML version deleted]] ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
