varCheck {glmxdiag}

Checking adequacy of variance function

Description

According to GLM theory, the true variance function can be estimated as (y-mu)^2/phi. Comparing this quantity with the variance function assumed by the model suggests if the chosen one is appropriate. If the model is correct, points should be arranged near the bisector; otherwise this plot suggests the direction of the error made by chosing the variance function.

Usage

varCheck(model, xlab, ylab, pch, col, lcol, ...)

Arguments

model

a model supported by glmxdiag.

xlab

title for the x axis.

ylab

title for the y axis.

pch

type of points.

col

color of the points.

lcol

color of the bisector.

...

further arguments passed to plot.

Value

Doesn't return a value, called for side effects.

Author(s)

Giuseppe Reale

Examples

data(stopping, package = 'glmxdiag')
mod <- glm(Distance ~ Speed, family = Gamma(link = 'sqrt'), data = stopping)
varCheck(mod)