Dear all, I'm using R to perform multiple comparison testing on agriculture genotype trials. To perform the Duncan's MRT, I use the qtukey() function with the following syntax:
qtukey(p = ((1 - 0.05) ^ (pos - 1)), nmeans = pos, df = ni) I experience a strange behaviour when the number of means in the trial and the number of residual degrees of freedom (ni) becomes high (orientatively pos > 30 and ni > 60), i.e. the function returns NaN together with the following message: convergence failed in 'qtukey' Running the code below should reproduce a statistical table for Duncan's MRT, such those reported on old books of agricultural statistics (ex. Steel and Torrie, 1960). table <- matrix(0, 28, 14) pos <- c(10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 50, 100, 200) df <- c(2:20, seq(22, 30, by = 2), 40, 60, 100, 1000) for (i in 1:28) table [i, ] <- qtukey(p = ((1 - 0.05) ^ (pos - 1)), nmeans = pos, df = df[i]) colnames(table) <- pos rownames(table) <- df Indeed, I get several NaN and some odd figures. Am I doing something wrong or is there any intrinsic limit for the values of p, nmeans and df within the qtukey() function? Just in this latter case, is it possible to raise those limits? Some genotype trials can have more than thirty treatments under comparison. I thank you all for your attention. Andrea Onofri Department of Agriculture and Environmental Sciences University of Perugia (ITALY) ______________________________________________ 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.
