leveneTest: Levene's Test

Description Usage Arguments Value Note Author(s) References Examples

Description

Computes Levene's test for homogeneity of variance across groups.

Usage

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leveneTest(y, ...)
## S3 method for class 'formula'
leveneTest(y, data, ...)
## S3 method for class 'lm'
leveneTest(y, ...)
## Default S3 method:
leveneTest(y, group, center=median, ...)

Arguments

y

response variable for the default method, or a lm or formula object. If y is a linear-model object or a formula, the variables on the right-hand-side of the model must all be factors and must be completely crossed.

group

factor defining groups.

center

The name of a function to compute the center of each group; mean gives the original Levene's test; the default, median, provides a more robust test.

data

a data frame for evaluating the formula.

...

arguments to be passed down, e.g., data for the formula and lm methods; can also be used to pass arguments to the function given by center (e.g., center=mean and trim=0.1 specify the 10% trimmed mean).

Value

returns an object meant to be printed showing the results of the test.

Note

adapted from a response posted by Brian Ripley to the r-help email list.

Author(s)

John Fox [email protected]; original generic version contributed by Derek Ogle

References

Fox, J. (2016) Applied Regression Analysis and Generalized Linear Models, Third Edition. Sage.

Fox, J. and Weisberg, S. (2019) An R Companion to Applied Regression, Third Edition, Sage.

Examples

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with(Moore, leveneTest(conformity, fcategory))
with(Moore, leveneTest(conformity, interaction(fcategory, partner.status)))
leveneTest(conformity ~ fcategory*partner.status, data=Moore)
leveneTest(lm(conformity ~ fcategory*partner.status, data=Moore))
leveneTest(conformity ~ fcategory*partner.status, data=Moore, center=mean)
leveneTest(conformity ~ fcategory*partner.status, data=Moore, center=mean, trim=0.1)

Example output

Levene's Test for Homogeneity of Variance (center = median)
      Df F value Pr(>F)
group  2   0.046 0.9551
      42               
Levene's Test for Homogeneity of Variance (center = median)
      Df F value Pr(>F)
group  5  1.4694 0.2219
      39               
Levene's Test for Homogeneity of Variance (center = median)
      Df F value Pr(>F)
group  5  1.4694 0.2219
      39               
Levene's Test for Homogeneity of Variance (center = median)
      Df F value Pr(>F)
group  5  1.4694 0.2219
      39               
Levene's Test for Homogeneity of Variance (center = mean)
      Df F value Pr(>F)
group  5  1.7915 0.1373
      39               
Levene's Test for Homogeneity of Variance (center = mean: 0.1)
      Df F value Pr(>F)
group  5  1.7962 0.1363
      39               

car documentation built on May 27, 2019, 5:02 p.m.