All - I think I'm being dense, but for the life of me, I can't figure out why I get error message with the code below. I have data that looks like param level perc.surv asin.tran DO 3 0.6864407 0.9764544 DO 3 0.1250000 0.3613671 DO 3 0.8738739 1.2077299 DO 4 0.4615385 0.7468986 DO 4 0.5691057 0.8547258 DO 4 0.8504673 1.1737517 DO 6 0.5494505 0.8349297 DO 6 0.4938272 0.7792252 DO 6 0.1230769 0.3584500 DO 6 0.7209302 1.0142339 DO 6 0.2297297 0.4998584 DO 6 0.9300000 1.3030330 DO 6 0.4482759 0.7335813 DO 6 0.0000000 0.0000000 DO 6 0.6018519 0.8879679 and code aov.DO <- aov(asin.tran~level) summary(aov.DO) TukeyHSD(aov.DO) When I run the final line, I get the following error message "Error in TukeyHSD.aov(aov.DO) : no factors in the fitted model In addition: Warning message: In replications(paste("~", xx), data = mf) : non-factors ignored: level" What am I missing? Thanks for your help - Steven Ranney steven.ranney at montana.edu