vocab1 <- read.table("c:/temp/vocabulary.txt",sep = "\t",header=T) # test of nonlinearity vocab1.lmlin <- lm(vocabulary ~ education, data=vocab1) summary(vocab1.lmlin) vocab1.lmsat <- lm(vocabulary ~ as.factor(education), data=vocab1) summary(vocab1.lmsat) anova(vocab1.lmlin,vocab1.lmsat) # using the car package to conduct Levene' test library(car) levene.test(vocabulary ~ as.factor(education), data=vocab1)