## Scale Parameter

A scale parameter is related to the
dispersion parameter and is given by
**Normal**

**Inverse Gaussian**

**Gamma**

**Poisson**
- 1

**Binomial**
- 1

The scale parameter is 1 for
Poisson and binomial distributions.
SAS/INSIGHT software provides different
scale parameter estimates for normal,
inverse Gaussian, and gamma distributions:

**MLE**
- the maximum-likelihood estimate

**Deviance**
- the mean deviance

**Pearson**
- the mean Pearson

**Constant**
- the value in the
**Constant** entry field

When maximum-likelihood estimation is used,
the Hessian **H** and the gradient **u**
also include the term for the scale parameter.
Note | You can request an exponential distribution for the response variable by
specifying a gamma distribution with scale parameter set to 1. |

Copyright © 1999 by SAS Institute Inc., Cary, NC, USA. All rights reserved.