# get our data
library("MASS")
attach(Melanoma)

# --------------------------------------------------------------------
# calculate mean and sd
# --------------------------------------------------------------------

# calculate the means by outcome
tapply(thickness, status, mean)

# calculate the sds by outcome
tapply(thickness, status, sd)


# --------------------------------------------------------------------
# perform Chi-Square test
# --------------------------------------------------------------------

# set up space in our matrix
M <- matrix(nrow=2, ncol=3, dimnames=list(c("ulcer", "no ulcer"), c("died of melanoma", "survived", "died of other causes")))

# get our totals for the matrix
M[["ulcer", "died of melanoma"]] 		<- length(which(ulcer==1 & status==1))
M[["ulcer", "survived"]] 				<- length(which(ulcer==1 & status==2))
M[["ulcer", "died of other causes"]] 	<- length(which(ulcer==1 & status==3))
M[["no ulcer", "died of melanoma"]] 	<- length(which(ulcer==0 & status==1))
M[["no ulcer", "survived"]] 			<- length(which(ulcer==0 & status==2))
M[["no ulcer", "died of other causes"]]	<- length(which(ulcer==0 & status==3))

# run the mighty chi-square test
print(chisq.test(M))
print(chisq.test(M, simulate.p.value=TRUE))

detach()