Test if k samples have equal variances
bartlett_test(variable, ...)
bartlett_test
returns an object of class "bartlett_test"
.
An object of class "bartlett_test"
is a list containing the
following components:
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.
Snedecor, George W. and Cochran, William G. (1989), Statistical Methods, Eighth Edition, Iowa State University Press.
# using grouping variable model <- lm(mpg ~ disp + hp, data = mtcars) resid <- residuals(model) cyl <- as.factor(mtcars$cyl) bartlett_test(resid, group_var = cyl)#> #> Bartlett's Test of Homogenity of Variances #> ------------------------------------------------ #> Ho: Variances are equal across groups #> Ha: Variances are unequal for atleast two groups #> #> Data #> ------------------------ #> Variable : resid #> Grouping Variable: cyl #> #> Test Summary #> ------------------------ #> DF = 2 #> Chi2 = 3.648 #> Prob > Chi2 = 0.161# using variables bartlett_test(hsb$read, hsb$write)#> #> Bartlett's Test of Homogenity of Variances #> ------------------------------------------------ #> Ho: Variances are equal across groups #> Ha: Variances are unequal for atleast two groups #> #> Data #> --------------------- #> Variables: read write #> #> Test Summary #> ------------------------ #> DF = 1 #> Chi2 = 1.223 #> Prob > Chi2 = 0.269# using formula mt <- mtcars mt$cyl <- as.factor(mt$cyl) bartlett_test(mpg ~ cyl, data = mt)#> #> Bartlett's Test of Homogenity of Variances #> ------------------------------------------------ #> Ho: Variances are equal across groups #> Ha: Variances are unequal for atleast two groups #> #> Data #> ---------------------------- #> Variable : var #> Grouping Variable: group_var #> #> Test Summary #> ------------------------ #> DF = 2 #> Chi2 = 8.393 #> Prob > Chi2 = 0.015# using model model <- lm(mpg ~ cyl, data = mt) bartlett_test(model)#> #> Bartlett's Test of Homogenity of Variances #> ------------------------------------------------ #> Ho: Variances are equal across groups #> Ha: Variances are unequal for atleast two groups #> #> Data #> ---------------------------- #> Variable : var #> Grouping Variable: group_var #> #> Test Summary #> ------------------------ #> DF = 2 #> Chi2 = 8.393 #> Prob > Chi2 = 0.015