levene_test reports Levene's robust test statistic for the equality of variances and the two statistics proposed by Brown and Forsythe that replace the mean in Levene's formula with alternative location estimators. The first alternative replaces the mean with the median. The second alternative replaces the mean with the 10

levene_test(variable, ...)

# S3 method for default
levene_test(variable, ..., group_var = NA,
  trim.mean = 0.1)

# S3 method for lm
levene_test(variable, ...)

# S3 method for formula
levene_test(variable, data, ...)

Arguments

variable
a numeric vector or formula or object of class lm
...
numeric vectors
group_var
a grouping variable
trim.mean
trimmed mean
data
a data frame

Value

levene_test returns an object of class "levene_test". An object of class "levene_test" is a list containing the following components:

References

Bland, M. 2000. An Introduction to Medical Statistics. 3rd ed. Oxford: Oxford University Press.

Brown, M. B., and A. B. Forsythe. 1974. Robust tests for the equality of variances. Journal of the American Statistical Association 69: 364–367.

Carroll, R. J., and H. Schneider. 1985. A note on Levene’s tests for equality of variances. Statistics and Probability Letters 3: 191–194.

Examples

# using grouping variable levene_test(hsb$read, group_var = hsb$race)
#> Summary Statistics #> Levels Frequency Mean Std. Dev #> ----------------------------------------- #> 1 24 46.67 10.24 #> 2 11 51.91 7.66 #> 3 20 46.8 7.12 #> 4 145 53.92 10.28 #> ----------------------------------------- #> Total 200 52.23 10.25 #> ----------------------------------------- #> #> Test Statistics #> ------------------------------------------------------------------------- #> Statistic Num DF Den DF F Pr > F #> ------------------------------------------------------------------------- #> Brown and Forsythe 3 196 3.44 0.0179 #> Levene 3 196 3.4792 0.017 #> Brown and Forsythe (Trimmed Mean) 3 196 3.3936 0.019 #> -------------------------------------------------------------------------
# using two variables levene_test(hsb$read, hsb$write, hsb$socst)
#> Summary Statistics #> Levels Frequency Mean Std. Dev #> ----------------------------------------- #> 0 200 52.23 10.25 #> 1 200 52.77 9.48 #> 2 200 52.41 10.74 #> ----------------------------------------- #> Total 600 52.47 10.15 #> ----------------------------------------- #> #> Test Statistics #> ------------------------------------------------------------------------- #> Statistic Num DF Den DF F Pr > F #> ------------------------------------------------------------------------- #> Brown and Forsythe 2 597 1.1683 0.3116 #> Levene 2 597 1.3803 0.2523 #> Brown and Forsythe (Trimmed Mean) 2 597 1.3258 0.2664 #> -------------------------------------------------------------------------
# using model m <- lm(read ~ female, data = hsb) levene_test(m)
#> Summary Statistics #> Levels Frequency Mean Std. Dev #> ----------------------------------------- #> 0 91 52.82 10.51 #> 1 109 51.73 10.06 #> ----------------------------------------- #> Total 200 52.23 10.25 #> ----------------------------------------- #> #> Test Statistics #> ------------------------------------------------------------------------- #> Statistic Num DF Den DF F Pr > F #> ------------------------------------------------------------------------- #> Brown and Forsythe 1 198 0.4542 0.5011 #> Levene 1 198 0.6024 0.4386 #> Brown and Forsythe (Trimmed Mean) 1 198 0.494 0.483 #> -------------------------------------------------------------------------
# using formula levene_test(as.formula(paste0('read ~ schtyp')), hsb)
#> Summary Statistics #> Levels Frequency Mean Std. Dev #> ----------------------------------------- #> 1 168 51.85 10.42 #> 2 32 54.25 9.2 #> ----------------------------------------- #> Total 200 52.23 10.25 #> ----------------------------------------- #> #> Test Statistics #> ------------------------------------------------------------------------- #> Statistic Num DF Den DF F Pr > F #> ------------------------------------------------------------------------- #> Brown and Forsythe 1 198 0.5643 0.4534 #> Levene 1 198 0.6153 0.4337 #> Brown and Forsythe (Trimmed Mean) 1 198 0.5886 0.4439 #> -------------------------------------------------------------------------