# Lifetime (in hours) for 4 different battery types

 source("http://www.uvm.edu/~rsingle/stat221/data/scripts-221.R")

#---Original Data
 dat5 = otherdata("battery2.dat")
 mod5 <- lm(hours ~ type, data=dat5)
 anova(mod5)
 
#Checking assumptions
 qqnorm(mod5$residuals); qqline(mod5$residuals)
 boxplot(mod5$residuals)
 boxplot(hours ~ type, data=dat5) 

#---Transformed Data (rank transformation)
 dat5$rank = rank(dat5$hours)
 mod6 <- lm(rank ~ type, data=dat5)
 anova(mod6)
 
#Checking assumptions
 qqnorm(mod6$residuals); qqline(mod6$residuals)
 boxplot(mod6$residuals)
 boxplot(rank ~ type, data=dat5) 

#---Kruskal-Wallis Rank Sum Non-parametric Test 
 kruskal.test(hours ~ type, data=dat5)

# also known as the Wilcoxon (Mann-Whitney) rank sum test
# for 2-sample comparisons