wle.t.test {wle} | R Documentation |
wle.t.test
performs one and two sample Weighted Likelihood t-tests on vectors of data. This is a robust version of the classical t-test. It should be used when the majority of the data follows a normal distribution.
wle.t.test(x, y = NULL, alternative = c("two.sided", "less", "greater"), mu = 0, paired = FALSE, var.equal = FALSE, conf.level = 0.95, boot=30, group, num.sol=1, raf="HD", smooth=0.003, tol=10^(-6), equal=10^(-3), max.iter=500)
x |
a numeric vector of data values. |
y |
an optional numeric vector data values. |
alternative |
character specifying the alternative hypothesis,
must be one of "two.sided" (default), "greater" or
"less" . You can specify just the initial letter. |
mu |
a number indicating the true value of the mean (or difference in means if you are performing a two sample test). |
paired |
a logical indicating whether you want a paired weighted t-test. |
var.equal |
a logical variable indicating whether to treat the
two variances as being equal. If TRUE then the pooled
variance is used to estimate the variance otherwise the Welch
approximation to the degrees of freedom is used. |
conf.level |
confidence level of the interval. |
boot |
the number of starting points based on boostrap subsamples to use in the search of the roots. |
group |
the dimension of the bootstap subsamples. The default value is max(round(size/4),2) where size is the number of observations. |
num.sol |
maximum number of roots to be searched. |
raf |
type of Residual adjustment function to be use:
raf="HD" : Hellinger Distance RAF,
raf="NED" : Negative Exponential Disparity RAF,
raf="SCHI2" : Symmetric Chi-Squared Disparity RAF. |
smooth |
the value of the smoothing parameter. |
tol |
the absolute accuracy to be used to achieve convergence of the algorithm. |
equal |
the absolute value for which two roots are considered the same. (This parameter must be greater than tol ). |
max.iter |
maximum number of iterations. |
If paired
is TRUE
then both x
and y
must
be specified and they must be the same length. Missing values are
removed (in pairs if paired
is TRUE
). If
var.equal
is TRUE
then the pooled estimate of the
variance is used. By default, if var.equal
is FALSE
then the variance is estimated separately for both groups and the
Welch modification to the degrees of freedom is used.
The function return a list of class "wle.t.test"
with the following components:
test |
A list with two dimensions. Each cell is related with a combination of 'x', 'y' roots. In each cell a list of class "htest" containing the following components:
statistic the value of the t-statistic.
parameters the degrees of freedom for the t-statistic.
p.value the p-value for the test.
conf.int a confidence interval for the mean appropriate to the specified alternative hypothesis.
estimate the estimated mean or difference in means depending on whether it was a one-sample test or a two-sample test.
null.value the specified hypothesized value of the mean or mean difference depending on whether it was a one-sample test or a two-sample test.
alternative a character string describing the alternative hypothesis.
method a character string indicating what type of t-test was performed.
data.name a character string giving the name(s) of the data.
x.weights the weights related to the 'x' data.
y.weights the weights related to the 'y' data.
x.root the number of the 'x' root.
y.root the number of the 'y' root.
|
x.tot.sol |
the number of solutions for the dataset 'x'. |
y.tot.sol |
the number of solutions for the dataset 'y' or 1. |
call |
the match.call(). |
paired |
a logical indicating whether is a paired weighted t-test. |
x |
'x' data. |
y |
'y' data or NULL . |
Claudio Agostinelli
Agostinelli, C., (1998) Inferenza statistica robusta basata sulla funzione di verosimiglianza pesata: alcuni sviluppi, Ph.D Thesis, Department of Statistics, University of Padova (in italian).
Agostinelli, C., (2002) Un approccio alla verifica d'ipotesi robusta basato sulla funzione di verosimiglianza pesata - Robust Testing Hypotheses via Weighted Likelihood function, Statistica, Anno LXII, 1, 87-110.
Agostinelli, C., and Markatou, M., (2001) Test of hypotheses based on the Weighted Likelihood Methodology, Statistica Sinica, vol. 11, n. 2, 499-514.
library(wle) set.seed(1234) x <- rnorm(20,0,1) y <- rnorm(20,6,1) t.test(x,y) # P < 2.2e-16 wle.t.test(x,y,group=5) # P < 2.2e-16 t.test(x,y=c(y,250)) # P = 0.1419 -- NOT significant anymore wle.t.test(x,y=c(y,250),group=5) # P < 2.2e-16 -- still significant set.seed(1234) # three roots for 'x' and three roots for 'y' # with nine t-test value res <- wle.t.test(x=c(rnorm(40,0,1),rnorm(40,10,1)), y=c(rnorm(40,0,1),rnorm(40,10,1)), group=4,num.sol=3,boot=100) print(res) # print ALL the t-test print(res,x.root=1,y.root=1) # print the test associated to the # x.root=1,y.root=1 root.1.1 <- res$test[[1]][[1]] # access to the object associated # to the x.root=1,y.root=1 names(root.1.1) set.seed(1234) # one root and NOT significant t-test wle.t.test(x=c(rnorm(40,0,1),rnorm(40,10,1)), y=c(rnorm(40,0,1),rnorm(40,10,1)), group=4,num.sol=3,boot=100,paired=TRUE)