snkTest: Student-Newman-Keuls Test

In PMCMRplus: Calculate Pairwise Multiple Comparisons of Mean Rank Sums Extended

Student-Newman-Keuls Test

Description

Performs Student-Newman-Keuls all-pairs comparisons test for normally distributed data with equal group variances.

Usage

snkTest(x, ...)

## Default S3 method:
snkTest(x, g, ...)

## S3 method for class 'formula'
snkTest(formula, data, subset, na.action, ...)

## S3 method for class 'aov'
snkTest(x, ...)

Arguments

x	a numeric vector of data values, a list of numeric data vectors or a fitted model object, usually an aov fit.
...	further arguments to be passed to or from methods.
g	a vector or factor object giving the group for the corresponding elements of "x". Ignored with a warning if "x" is a list.
formula	a formula of the form response ~ group where response gives the data values and group a vector or factor of the corresponding groups.
data	an optional matrix or data frame (or similar: see model.frame) containing the variables in the formula formula. By default the variables are taken from environment(formula).
subset	an optional vector specifying a subset of observations to be used.
na.action	a function which indicates what should happen when the data contain NAs. Defaults to getOption("na.action").

Details

For all-pairs comparisons in an one-factorial layout with normally distributed residuals and equal variances Student-Newman-Keuls test can be performed. A total of m = k(k-1)/2 hypotheses can be tested. The null hypothesis H_{ij}: \mu_i(x) = \mu_j(x) is tested in the two-tailed test against the alternative A_{ij}: \mu_i(x) \ne \mu_j(x), ~~ i \ne j.

The p-values are computed from the Tukey-distribution.

Value

A list with class "PMCMR" containing the following components:

method

a character string indicating what type of test was performed.

data.name

a character string giving the name(s) of the data.

statistic

lower-triangle matrix of the estimated quantiles of the pairwise test statistics.

p.value

lower-triangle matrix of the p-values for the pairwise tests.

alternative

a character string describing the alternative hypothesis.

p.adjust.method

a character string describing the method for p-value adjustment.

model

a data frame of the input data.

dist

a string that denotes the test distribution.

References

Keuls, M. (1952) The use of the "studentized range" in connection with an analysis of variance, Euphytica 1, 112–122.

Newman, D. (1939) The distribution of range in samples from a normal population, expressed in terms of an independent estimate of standard deviation, Biometrika 31, 20–30.

Student (1927) Errors of routine analysis, Biometrika 19, 151–164.

See Also

Tukey, TukeyHSD tukeyTest

Examples

fit <- aov(weight ~ feed, chickwts)
shapiro.test(residuals(fit))
bartlett.test(weight ~ feed, chickwts)
anova(fit)

## also works with fitted objects of class aov
res <- snkTest(fit)
summary(res)
summaryGroup(res)

PMCMRplus documentation built on May 29, 2024, 8:34 a.m.