Likelihood Ratio Test for nested iZIP models

Perform a likelihood ratio chi-squared test between nested iZIP models. The test statistics is calculated as 2*(llik- llik_0). The test statistics has degrees of freedom r where r is the difference in the number of parameters between the full and null models.

iziplrtest(object1, object2, digits = 3)

Arguments

object1	an object class 'izip', obtained from a call to glm.izip
object2	an object class 'izip', obtained from a call to glm.izip
digits	numeric; minimum number of significant digits to be used for most numbers.

See also

glm.izip, update.izip

Examples

data(bioChemists)

## Fit full model
M_bioChem.full <- glm.izip(art ~ ., data = bioChemists)

## Fit null model; without phd
M.bioChem.null <- update(M_bioChem.full, . ~ . - phd)

## Likelihood ratio test for the nested models
iziplrtest(M_bioChem.full, M.bioChem.null) # order of objects is not important
#> 
#> Likelihood ratio test for testing both iZIP models are equivalent
#> LRT-statistic:  0.111 
#> Chi-sq degrees of freedom:  1 
#> P-value:  0.739