modlevenes.test {asbio}R Documentation

Modified Levene's test

Description

Conducts the modifies Levene's test for homoscedastic populations.

Usage


modlevenes.test(x, groups)

Arguments

x Vector of residuals from a linear model.
groups Vector of factor levels.

Details

The modified Levene's test is a test for homoscedsticity that (unlike the classic F-test) is robust to violations of normality (Conover et al. 1981). In a Modified Levene's test we calculate d_{ij}=|e_{ij} - tilde{e}_{i}| where tilde{e}_i is the ith factor level residual median. We then run an ANOVA on the d_{ij}'s. If the p-value is < α, we reject the null and conclude that the population error variances are not equal.

Value

An ANOVA table is returned with the modified Levene's test results.

Author(s)

Ken Aho

References

Kutner, M. H., Nachtsheim, C. J., Neter, J., and W. Li. (2005) Applied linear statistical models, 5th edition. McGraw-Hill, Boston.

See Also

fligner.test

Examples

eggs<-c(11,17,16,14,15,12,10,15,19,11,23,20,18,17,27,33,22,26,28)
trt<-as.factor(c(1,1,1,1,1,2,2,2,2,2,3,3,3,3,4,4,4,4,4))
lm1<-lm(eggs~trt)
modlevenes.test(residuals(lm1),trt)


[Package asbio version 0.1 Index]