Test if k samples are from populations with equal variances.
Usage
ols_test_bartlett(data, ...)
# Default S3 method
ols_test_bartlett(data, ..., group_var = NULL)Value
ols_test_bartlett returns an object of class "ols_test_bartlett".
An object of class "ols_test_bartlett" is a list containing the
following components:
- fstat
f statistic
- pval
p-value of
fstat- df
degrees of freedom
Details
Bartlett's test is used to test if variances across samples is equal. It is sensitive to departures from normality. The Levene test is an alternative test that is less sensitive to departures from normality.
References
Snedecor, George W. and Cochran, William G. (1989), Statistical Methods, Eighth Edition, Iowa State University Press.
See also
Other heteroskedasticity tests:
ols_test_breusch_pagan(),
ols_test_f(),
ols_test_score()
Examples
# using grouping variable
if (require("descriptr")) {
library(descriptr)
ols_test_bartlett(mtcarz, 'mpg', group_var = 'cyl')
}
#> Loading required package: descriptr
#>
#> Attaching package: 'descriptr'
#> The following object is masked from 'package:olsrr':
#>
#> hsb
#>
#> Bartlett's Test of Homogenity of Variances
#> ------------------------------------------------
#> Ho: Variances are equal across groups
#> Ha: Variances are unequal for atleast two groups
#>
#> Test Summary
#> -----------------------------
#> DF = 2
#> Chi2 = 8.39345
#> Prob > Chi2 = 0.01504477
# using variables
ols_test_bartlett(hsb, 'read', 'write')
#>
#> Bartlett's Test of Homogenity of Variances
#> ------------------------------------------------
#> Ho: Variances are equal across groups
#> Ha: Variances are unequal for atleast two groups
#>
#> Data
#> ---------------------
#> Variables: read write
#>
#> Test Summary
#> ----------------------------
#> DF = 1
#> Chi2 = 1.222871
#> Prob > Chi2 = 0.2687979