dispersion_params {spmodel} | R Documentation |
Create a dispersion parameter object
Description
Create a dispersion parameter object for use with other functions.
Usage
dispersion_params(family, dispersion)
Arguments
family |
The generalized linear model family describing the distribution
of the response variable to be used. |
dispersion |
The value of the dispersion parameter. |
Details
The variance function of an individual (given
)
for each generalized linear model family is given below:
family:
poisson:
nbinomial:
binomial:
beta:
Gamma:
inverse.gaussian:
The parameter is a dispersion parameter that influences
.
For the
poisson
and binomial
families, is always
one. Note that this inverse Gaussian parameterization is different than a
standard inverse Gaussian parameterization, which has variance
.
Setting
yields our parameterization, which is
preferred for computational stability. Also note that the dispersion parameter
is often defined in the literature as
, where
is the variance
function of the mean. We do not use this parameterization, which is important
to recognize while interpreting dispersion parameter estimates using
spglm()
or spgautor()
.
For more on generalized linear model constructions, see McCullagh and
Nelder (1989).
Value
A named numeric vector with class family
containing the dispersion.
References
McCullagh P. and Nelder, J. A. (1989) Generalized Linear Models. London: Chapman and Hall.
Examples
dispersion_params("beta", dispersion = 1)