Testing the difference between two CV's

Asset.R

#-----------------------------------------------------------------------------
# Testing the difference between two CV's
# From Example 8.12 in Zar, p. 144-145
#-----------------------------------------------------------------------------
w<-c(72.5,71.5,60.8,63.2,71.4,73.1,77.9,75.7,72.0,69.0)
h<-c(183.0,172.3,180.1,190.2,191.4,169.6,166.4,177.6,184.7,187.5,179.8)
#-----------------------------------------------------------------------------
# Testing the difference between two CV's
library(MBESS)
n1<-length(w); n2<-length(h)
v1<-cv(mean=mean(w,na.rm=T), sd=var(w,na.rm=T)^.5, N=n1, unbiased=TRUE)
v2<-cv(mean=mean(h,na.rm=T), sd=var(h,na.rm=T)^.5, N=n2, unbiased=TRUE)

# Formula in Example 8.12 of Zar, p. 145
vp<-(((n1-1)*v1)+((n2-1)*v2))/((n1-1)+(n2-1))
Z<-(v1-v2)/(sqrt((vp^2/(n1-1))+(vp^2/(n2-1))*(0.5+vp^2)))
# P for z value
2*(1-pt(Z,2))
#-----------------------------------------------------------------------------
# Confidence intervals for the CV's
library(MBESS)
set.seed(113)
n1<-length(data$w)
meanX<-mean(data$w,na.rm=T)
sdX <- var(data$w,na.rm=T)^.5

ci.cv(mean=meanX, sd=sdX, n=n1, alpha.lower=.025, alpha.upper=.025,
conf.level=NULL)

#-----------------------------------------------------------------------------
# Variance test
F<-var(data$w,na.rm=T)/var(data$h,na.rm=T)
2*(1-pf(F,length(data$w)-1,length(data$h)-1))

var.test(data$w,data$h)