RVAideMemoire (version 0.9-45-2)

perm.var.test: Permutational F test to compare two variances

Description

Performs a permutational F test to compare two variances.

Usage

perm.var.test(x, ...)

## S3 method for class 'default':
perm.var.test(x, y, ...)

## S3 method for class 'formula':
perm.var.test(formula, data, alternative = c("two.sided", "less",
  "greater"), nperm = 999, ...)

Arguments

x

a numeric vector of data values.

y

a numeric vector of data values.

formula

a formula of the form a ~ b where a gives the data values and b a factor with 2 levels giving the corresponding groups.

data

an optional data frame containing the variables in the formula formula. By default the variables are taken from environment(formula).

alternative

a character string specifying the alternative hypothesis, must be one of "two.sided" (default), "greater" or "less".

nperm

number of permutations.

...

further arguments to be passed to or from other methods.

Value

• method
  name of the test.
• statistic
  test statistics of the parametric test.
• permutations
  number of permutations.
• p.value
  p-value of the permutational test.
• estimate
  the ratio of the two variances.
• alternative
  a character string describing the alternative hypothesis.
• data.name
  a character string giving the name(s) of the data.
• null.value
  the ratio of population variances under the null hypothesis, always 1.

Details

The function deals with the limitted floating point precision, which can bias calculation of p-values based on a discrete test statistic distribution.

See Also

var.test

Examples

response <- c(rpois(8,1),rpois(8,3))
fact <- gl(2,8,labels=LETTERS[1:2])
perm.var.test(response~fact)