Performs Student-Newman-Keuls all-pairs comparisons test for normally distributed data with equal group variances.
snkTest(x, ...)# S3 method for default
snkTest(x, g, ...)
# S3 method for formula
snkTest(formula, data, subset, na.action, ...)
# S3 method for aov
snkTest(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.
a vector or factor object giving the group for the
corresponding elements of "x".
Ignored with a warning if "x" is a list.
a formula of the form response ~ group where
response gives the data values and group a vector or
factor of the corresponding groups.
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).
an optional vector specifying a subset of observations to be used.
a function which indicates what should happen when
the data contain NAs. Defaults to getOption("na.action").
A list with class "PMCMR" containing the following components:
a character string indicating what type of test was performed.
a character string giving the name(s) of the data.
lower-triangle matrix of the estimated quantiles of the pairwise test statistics.
lower-triangle matrix of the p-values for the pairwise tests.
a character string describing the alternative hypothesis.
a character string describing the method for p-value adjustment.
a data frame of the input data.
a string that denotes the test distribution.
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.
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.
# NOT RUN {
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)
# }
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