#Biostatistics 170

#READING DATA IN R FORMAT:

ZAR=read.table("ZarEX8.7R.txt")
ZAR
attach(ZAR)

X1=data[type=="typ1"]
X1
X2=data[type=="typ2"]
X2

#PERFORMING F TEST FOR EQUAL VARIANCES
?var.test

#TWO-SIDED CASE:

var.test(X1,X2,alternative="two.sided",conf.level=0.95)

#NOTE ALTERNATIVE COMMAND IN R 
#FOR THE SAME TEST:

var.test(data~type,alternative="two.sided",conf.level=0.95)  

#ONE-SIDED CASE LOWER TAIL:

var.test(data~type,alternative="less",conf.level=0.95)  

#ONE-SIDED CASE UPPER TAIL:

var.test(data~type,alternative="greater",conf.level=0.95)  

#PERFORMING LEVENE TEST FOR EQUAL VARIANCES
#DOWNLOAD {car} FROM CRAN WEBSITE
library(car)

?leveneTest
leveneTest(data,type,center=mean)
leveneTest(data,type,center=median)