| imam.Var.test | R Documentation |
Robust test of scale for paired samples based on absolute deviations from the trimmed means (or medians), called Imam test in Wilcox (1989).
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, ...)
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. |
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.
A list with class "htest" containing the components of a paired t test.
Stephane CHAMPELY
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.
Var.test, grambsch.Var.test
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)