ifr_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
Usage
ifr_levene_test(data, ...)
# Default S3 method
ifr_levene_test(data, ..., group_var = NULL, trim_mean = 0.1)Value
ifr_levene_test returns an object of class "ifr_levene_test".
An object of class "ifr_levene_test" is a list containing the
following components:
- bf
Brown and Forsythe f statistic
- p_bf
p-value for Brown and Forsythe f statistic
- lev
Levene's f statistic
- p_lev
p-value for Levene's f statistic
- bft
Brown and Forsythe f statistic using trimmed mean
- p_bft
p-value for Brown and Forsythe f statistic using trimmed mean
- avgs
mean for each level of the grouping variable
- sds
standard deviations for each level of the grouping variable
- avg
combined mean
- sd
combined standard deviation
- n
number of observations
- n_df
numerator degrees of freedom
- d_df
denominator degrees of freedom
- levs
levels of the grouping variable
- lens
number of observations for each level of the grouping variable
- type
alternative hypothesis
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
ifr_levene_test(hsb, read, group_var = 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 variables
ifr_levene_test(hsb, read, write, 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
#> -------------------------------------------------------------------------