imam.Var.test: Imam test of scale for paired samples

In PairedData: Paired Data Analysis

Description

Robust test of scale for paired samples based on absolute deviations from the trimmed means (or medians), called Imam test in Wilcox (1989).

Usage

imam.Var.test(x, ...)

## Default S3 method:
imam.Var.test(x, y = NULL,
       alternative = c("two.sided", "less", "greater"),
       mu = 0,conf.level = 0.95,location=c("trim","median"),
tr=0.1,  ...)


## S3 method for class 'paired'
imam.Var.test(x, ...)

Arguments

x	first sample or object of class paired.
y	second sample.
alternative	alternative hypothesis.
mu	the location parameter mu.
conf.level	confidence level.
location	location parameter for centering: trimmed mean or median.
tr	percentage of trimming.
...	further arguments to be passed to or from methods.

Details

The data are transformed as deviations from the trimmed mean: X=abs(x-mean(x,tr=0.1)) and Y=(y-mean(y,tr=0.1)). A paired t test is then carried out on the (global) ranks of X and Y.

Value

A list with class "htest" containing the components of a paired t test.

Author(s)

Stephane CHAMPELY

References

• Wilcox, R.R. (1989) Comparing the variances of dependent groups. Psychometrika, 54, 305-315.

• Conover, W.J. and Iman, R.L. (1981) Rank transformations as a bridge between parametric and nonparametric statistics. The American Statistician, 35, 124-129.

See Also

Var.test, grambsch.Var.test

Examples

z<-rnorm(20)
x<-rnorm(20)+z
y<-(rnorm(20)+z)*2
imam.Var.test(x,y)

# some variations
imam.Var.test(x,y,tr=0.2)
imam.Var.test(x,y,location="median")

data(anscombe2)
p<-with(anscombe2,paired(X1,Y1))
imam.Var.test(p)

Example output

Loading required package: MASS
Loading required package: gld
Loading required package: mvtnorm
Loading required package: lattice
Loading required package: ggplot2

Attaching package: 'PairedData'

The following object is masked from 'package:base':

    summary


	Imam paired test for scale comparison

data:  x and y
t = -2.7269, df = 19, p-value = 0.01339
alternative hypothesis: true difference in means is not equal to 0
95 percent confidence interval:
 -15.73112  -2.06888
sample estimates:
mean of the differences 
                   -8.9 


	Imam paired test for scale comparison

data:  x and y
t = -2.6612, df = 19, p-value = 0.01543
alternative hypothesis: true difference in means is not equal to 0
95 percent confidence interval:
 -15.721152  -1.878848
sample estimates:
mean of the differences 
                   -8.8 


	Imam paired test for scale comparison

data:  x and y
t = -2.8402, df = 19, p-value = 0.01046
alternative hypothesis: true difference in means is not equal to 0
95 percent confidence interval:
 -14.763907  -2.236093
sample estimates:
mean of the differences 
                   -8.5 


	Imam paired test for scale comparison

data:  X1 and Y1
t = 0.032339, df = 14, p-value = 0.9747
alternative hypothesis: true difference in means is not equal to 0
95 percent confidence interval:
 -4.354759  4.488093
sample estimates:
mean of the differences 
             0.06666667 

PairedData documentation built on May 1, 2019, 6:49 p.m.