Im trying to run a model with a response variable p and 3 fixed factors to get ANOVA. this is how my code looks like : #run it as 3 fixed factor model p1=c(37,38,37,41,41,40,41,42,41) p2=c(42,41,43,42,42,42,43,42,43) p3=c(30,31,31,31,31,31,29,30,28) p4=c(42,43,42,43,43,43,42,42,42) p5=c(28,30,29,29,30,29,31,29,29) p6=c(42,42,43,45,45,45,44,46,45) p7=c(25,26,27,28,28,30,29,27,27) p8=c(40,40,40,43,42,42,43,43,41) p9=c(37,38,37,41,41,40,41,42,41) p10=c(35,34,34,35,35,34,35,34,35) p = cbind(p1,p2,p3,p4,p5,p6,p7,p8,p9,p10) partnumber=c(rep(1,9),rep(2,9),rep(3,9),rep(4,9),rep(5,9),rep(6,9),rep(7,9),rep(8,9),rep(9,9),rep(10,9)) test=c(rep(c(rep(1:3,3)),10)) inspector = rep(c(rep(1,3),rep(2,3),rep(3,3)),10) fpartnumber = factor(partnumber) ftest = factor(test) finspector = factor(inspector) model=lm(p~fpartnumber*ftest*finspector) summary(model) anova(model) but when I run it I get this error : it says my variable length for fpartnumber is different , but when I checked the length of each variable and is 90. What is going on ? model=lm(y~fpartnumber*ftest*finspector) Error in model.frame.default(formula = yang ~ fpartnumber * ftest * finspector, : variable lengths differ (found for 'fpartnumber')