obrien.test {vartest}

O'Brien Test

Description

obrien.test performs O'Brien variance homogeneity test.

Usage

obrien.test(formula, data, center = "mean", trim.rate = 0.25, alpha = 0.05, 
  na.rm = TRUE, verbose = TRUE)

Arguments

formula

a formula of the form lhs ~ rhs where lhs gives the sample values and rhs the corresponding groups.

data

a tibble or data frame containing the variables in formula.

center

a character string to define how to center. "mean": mean, "median": median, and "trim.mean": trimmed mean.

trim.rate

the rate of observations trimmed from each tail of the distribution. Default is set to 0.25.

alpha

the level of significance to assess variance homogeneity. Default is set to alpha = 0.05.

na.rm

a logical value indicating whether NA values should be stripped before the computation proceeds.

verbose

a logical for printing output to R console.

Value

A list containing the following components:

statistic

the corresponding test statistic.

parameter

the parameter(s) of the approximate F distribution of the test statistic.

p.value

the p-value of the test.

method

the character string "O'Brien Test".

data

a data frame containing the variables in which NA values (if exist) are removed.

formula

a formula of the form lhs ~ rhs where lhs gives the sample values and rhs the corresponding groups.

Author(s)

Gozde Cosar and Osman Dag

References

O'Brien, R.G. (1981). A Simple Test for Variance Effects in Experimental Designs. Psychological Bulletin, 89:3, 570-574.

Gorbunova, A.A., Lemeshko, B.Y. (2012). Application of Parametric Homogeneity of Variances Tests under Violation of Classical Assumption. 2nd Stochastic Modeling Techniques and Data Analysis International Conference, 5:8, 253-260.

Examples

library(vartest)

obrien.test(Sepal.Length ~ Species, data = iris, center="mean")