anova.negbin              package:MASS              R Documentation

Likelihood Ratio Tests for Negative Binomial GLMs

Description:

     Method function to perform sequential likelihood ratio tests for
     Negative Binomial generalized linear models.

Usage:

     ## S3 method for class 'negbin':
     anova(object, ..., test = "Chisq")

Arguments:

  object: Fitted model object of class '"negbin"', inheriting from
          classes '"glm"' and '"lm"', specifying a Negative Binomial
          fitted GLM.  Typically the output of 'glm.nb()'. 

     ...: Zero or more additional fitted model objects of class
          '"negbin"'.  They should form a nested sequence of models,
          but need not be specified in any particular order. 

    test: Argument to match the 'test' argument of 'anova.glm'. Ignored
          (with a warning if changed) if a sequence of two or more
          Negative Binomial fitted model objects is specified, but
          possibly used if only one object is specified. 

Details:

     This function is a method for the generic function 'anova()' for
     class '"negbin"'. It can be invoked by calling 'anova(x)' for an
     object 'x' of the appropriate class, or directly by calling
     'anova.negbin(x)' regardless of the class of the object.

Note:

     If only one fitted model object is specified, a sequential
     analysis of deviance table is given for the fitted model.  The
     'theta' parameter is kept fixed.  If more than one fitted model
     object is specified they must all be of class '"negbin"' and
     likelihood ratio tests are done of each model within the next.  In
     this case 'theta' is assumed to have been re-estimated for each
     model.

References:

     Venables, W. N. and Ripley, B. D. (2002) _Modern Applied
     Statistics with S._ Fourth edition.  Springer.

See Also:

     'glm.nb', 'negative.binomial', 'summary.negbin'

Examples:

     m1 <- glm.nb(Days ~ Eth*Age*Lrn*Sex, quine, link = log)
     m2 <- update(m1, . ~ . - Eth:Age:Lrn:Sex)
     anova(m2, m1)
     anova(m2)

