# R-program for Exercise 27.8 of PSLS 3e

corn <- read.csv("h:/vhm/vhm801/Datasets/csv/Chapter 27/ex27_008.csv")
corn09 <- corn[corn$weeds==0 | corn$weeds==9,]

# Mann-Whitney-Wilcoxon 2-sample test (or Wilcoxon rank sum test)
wilcox.test( yield~ as.factor(weeds), data=corn09)
wilcox.test( yield~ as.factor(weeds), data=corn09, exact=T, conf.int=T)

# two-sample t-test
t.test( yield~ as.factor(weeds), data=corn09)

# analyses without outlier
wilcox.test( yield~ as.factor(weeds), data=corn09[corn09$yield>150,])
t.test( yield~ as.factor(weeds), data=corn09[corn09$yield>150,])