Hi It looks like the na.rm flag is not working in function weighted.mean. > weighted.mean(mat95$U,mat95$fpanual) [1] NA > weighted.mean(mat95$U,mat95$fpanual,na.rm=TRUE) [1] NA > mat95 <- mat95[!is.na(mat95$fpanual),] > weighted.mean(mat95$U,mat95$fpanual) [1] 14.93259 Regards EJ