A list with class "vht" 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.
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.
Author
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.
library(vartest)
obrien.test(Sepal.Length ~ Species, data = iris, center = "mean")
out <- obrien.test(Sepal.Length ~ Species, data = iris, center = "mean")
summary(out)