You can also get CIs for medians as a side effect of boxplot. If for some reason you need to get the same result as you would get from SAS, you could use the following (non-optimised but hopefully intelligible) instead.
HTH ############################################### # 95% confidence interval function for the median # prints out CI, returns invisible list of median.hat, lowlim, highlim # matches the output of SAS proc FREQ CIPCTLDF option ############################################### # "ci.median.sas" <- function(x, do.print=TRUE) { x <- x[!is.na(x)] median.hat <- median(x) nobs <- length(x) x.ranked <- sort(x) if (nobs < 2 ) { if (do.print) print(paste(median.hat, " (---, ---)", sep = "")) invisible(return(median.hat, lowlim=NA, highlim=NA)) } # in general, rank of low cutoff point is the position of q in 0:nobs, so add one # to give the position in 1:nobs lowrank <- qbinom(0.025, nobs, 0.5) + 1 # but make sure that this choice does not use up too much probability, making a # 95% interval impossible (except for very small samples, low will always be one): plow <- pbinom(lowrank-1, nobs, 0.5) if (plow > 0.05 && lowrank > 1) { lowrank <- lowrank - 1 plow <- pbinom(lowrank-1, nobs, 0.5) } # then find the corresponding high cutoff giving (better than) 95% coverage overall: # nb for very small samples plow will still exceed 0.05, so we use min(1,p) to # prevent potential eror highrank <- qbinom(min(1, 0.95+plow), nobs, 0.5) + 1 # again +1 for index in 1:nobs rather than 0:nobs lowlim <- x.ranked[lowrank] highlim <- x.ranked[min(highrank, nobs)] if (do.print) print(paste(median.hat, " (", lowlim, ", ", highlim, ")", sep = "")) invisible(return(median.hat, lowlim, highlim)) } Simon Fear Senior Statistician Syne qua non Ltd Tel: +44 (0) 1379 644449 Fax: +44 (0) 1379 644445 email: [EMAIL PROTECTED] web: http://www.synequanon.com Number of attachments included with this message: 0 This message (and any associated files) is confidential and\...{{dropped}} ______________________________________________ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help