ncvTest

0th

Percentile

Score Test for Non-Constant Error Variance

Computes a score test of the hypothesis of constant error variance against the alternative that the error variance changes with the level of the response (fitted values), or with a linear combination of predictors.

Keywords
regression, htest
Usage
ncvTest(model, ...)

# S3 method for lm ncvTest(model, var.formula, ...)

# S3 method for glm ncvTest(model, ...) # to report an error

Arguments
model

a weighted or unweighted linear model, produced by lm.

var.formula

a one-sided formula for the error variance; if omitted, the error variance depends on the fitted values.

arguments passed down to methods functions; not currently used.

Details

This test is often called the Breusch-Pagan test; it was independently suggested with some extension by Cook and Weisberg (1983).

ncvTest.glm is a dummy function to generate an error when a glm model is used.

Value

The function returns a chisqTest object, which is usually just printed.

References

Breusch, T. S. and Pagan, A. R. (1979) A simple test for heteroscedasticity and random coefficient variation. Econometrica 47, 1287--1294.

Cook, R. D. and Weisberg, S. (1983) Diagnostics for heteroscedasticity in regression. Biometrika 70, 1--10.

Fox, J. (2008) Applied Regression Analysis and Generalized Linear Models, Second Edition. Sage.

Fox, J. and Weisberg, S. (2011) An R Companion to Applied Regression, Second Edition, Sage.

Weisberg, S. (2014) Applied Linear Regression, Fourth Edition, Wiley.

See Also

hccm, spreadLevelPlot

Aliases
  • ncvTest
  • ncvTest.lm
  • ncvTest.glm
Examples
library(car) ncvTest(lm(interlocks ~ assets + sector + nation, data=Ornstein)) ncvTest(lm(interlocks ~ assets + sector + nation, data=Ornstein), ~ assets + sector + nation, data=Ornstein)
Documentation reproduced from package car, version 2.1-4, License: GPL (>= 2)

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