How to perform a mean comparison in R, with a treatment factor, that have 3 levels? -

can please me understand how perform comparison of means in r? treatment factor has 3 levels , want compare mean of yield @ each level of treatment factor significance

how write argument make r understand should compare mean.yield when treatment=75 (is factor, not numeric) mean.yield when treatment=100 , when treatment=125?

you can all-pairwise comparison using multcomp package.

library(multcomp)  mydata <- data.frame(treatment=c("75", "100", "125","75", "100", "125","75", "100", "125"),                      mean.yield=c(10,20,30,20,25,27,3,15,12))  immer.aov <- aov(mean.yield ~ treatment, data = mydata) immer.mc  <- glht(immer.aov, linfct = mcp(treatment = "tukey"))  summary(immer.mc)       

   simultaneous tests general linear hypotheses  multiple comparisons of means: tukey contrasts   fit: aov(formula = mean.yield ~ treatment, data = mydata)  linear hypotheses:                estimate std. error t value pr(>|t|) 125 - 100 == 0    3.000      6.515   0.460    0.892 75 - 100 == 0    -9.000      6.515  -1.381    0.407 75 - 125 == 0   -12.000      6.515  -1.842    0.235 (adjusted p values reported -- single-step method) 

for more details , options please check out package documentation , this resource.