var_test
performs tests on the equality of standard
deviations (variances).
var_test(variable, ..., group_var = NA, alternative = c("less", "greater", "all"))
var_test
returns an object of class "var_test"
.
An object of class "var_test"
is a list containing the
following components:
Sheskin, D. J. 2007. Handbook of Parametric and Nonparametric Statistical Procedures, 4th edition. : Chapman & Hall/CRC.
# using grouping variable # lower tail var_test(mtcars$mpg, group_var = mtcars$vs, alternative = 'less')#> Variance Ratio Test #> -------------------------------------------------- #> Group Obs Mean Std. Err. Std. Dev. #> -------------------------------------------------- #> 0 18 16.62 0.91 3.86 #> 1 14 24.56 1.44 5.38 #> -------------------------------------------------- #> combined 32 20.09 1.07 6.03 #> -------------------------------------------------- #> #> Lower Tail Test #> --------------- #> ratio = sd(0) / (1) #> Ho: ratio = 1 #> Ha: ratio < 1 #> #> Variance Ratio Test #> ------------------------------------ #> F Num DF Den DF p #> ------------------------------------ #> 0.5151 17 13 0.0999 #> ------------------------------------# upper tail var_test(mtcars$mpg, group_var = mtcars$vs, alternative = 'greater')#> Variance Ratio Test #> -------------------------------------------------- #> Group Obs Mean Std. Err. Std. Dev. #> -------------------------------------------------- #> 0 18 16.62 0.91 3.86 #> 1 14 24.56 1.44 5.38 #> -------------------------------------------------- #> combined 32 20.09 1.07 6.03 #> -------------------------------------------------- #> #> Upper Tail Test #> --------------- #> Ho: ratio = 1 #> Ha: ratio > 1 #> #> Variance Ratio Test #> ------------------------------------ #> F Num DF Den DF p #> ------------------------------------ #> 0.5151 17 13 0.9001 #> ------------------------------------# all tails var_test(mtcars$mpg, group_var = mtcars$vs, alternative = 'all')#> Variance Ratio Test #> -------------------------------------------------- #> Group Obs Mean Std. Err. Std. Dev. #> -------------------------------------------------- #> 0 18 16.62 0.91 3.86 #> 1 14 24.56 1.44 5.38 #> -------------------------------------------------- #> combined 32 20.09 1.07 6.03 #> -------------------------------------------------- #> #> Variance Ratio Test #> -------------------------------------------------- #> F Num DF Den DF #> -------------------------------------------------- #> 0.5151 17 13 #> -------------------------------------------------- #> #> Null & Alternate Hypothesis #> ---------------------------------------- #> ratio = sd(0) / (1) #> Ho: ratio = 1 #> #> Ha: ratio < 1 Ha: ratio > 1 #> Pr(F < f) = 0.0999 Pr(F > f) = 0.9001 #> ----------------------------------------# using two variables # lower tail var_test(hsb$read, hsb$write, alternative = 'less')#> Variance Ratio Test #> -------------------------------------------------- #> Group Obs Mean Std. Err. Std. Dev. #> -------------------------------------------------- #> read 200 52.23 0.72 10.25 #> write 200 52.77 0.67 9.48 #> -------------------------------------------------- #> combined 400 52.5 0.49 9.86 #> -------------------------------------------------- #> #> Lower Tail Test #> --------------- #> ratio = sd(read) / (write) #> Ho: ratio = 1 #> Ha: ratio < 1 #> #> Variance Ratio Test #> ------------------------------------ #> F Num DF Den DF p #> ------------------------------------ #> 1.1701 199 199 0.8656 #> ------------------------------------# upper tail var_test(hsb$read, hsb$write, alternative = 'greater')#> Variance Ratio Test #> -------------------------------------------------- #> Group Obs Mean Std. Err. Std. Dev. #> -------------------------------------------------- #> read 200 52.23 0.72 10.25 #> write 200 52.77 0.67 9.48 #> -------------------------------------------------- #> combined 400 52.5 0.49 9.86 #> -------------------------------------------------- #> #> Upper Tail Test #> --------------- #> Ho: ratio = 1 #> Ha: ratio > 1 #> #> Variance Ratio Test #> ------------------------------------ #> F Num DF Den DF p #> ------------------------------------ #> 1.1701 199 199 0.1344 #> ------------------------------------# all tails var_test(hsb$read, hsb$write, alternative = 'all')#> Variance Ratio Test #> -------------------------------------------------- #> Group Obs Mean Std. Err. Std. Dev. #> -------------------------------------------------- #> read 200 52.23 0.72 10.25 #> write 200 52.77 0.67 9.48 #> -------------------------------------------------- #> combined 400 52.5 0.49 9.86 #> -------------------------------------------------- #> #> Variance Ratio Test #> -------------------------------------------------- #> F Num DF Den DF #> -------------------------------------------------- #> 1.1701 199 199 #> -------------------------------------------------- #> #> Null & Alternate Hypothesis #> ---------------------------------------- #> ratio = sd(read) / (write) #> Ho: ratio = 1 #> #> Ha: ratio < 1 Ha: ratio > 1 #> Pr(F < f) = 0.8656 Pr(F > f) = 0.1344 #> ----------------------------------------