# RE : [R] Dispersion parameter in Neg Bin GLM

From: Lesnoff, Matthieu (ILRI) <m.lesnoff_at_cgiar.org>
Date: Thu 30 Jun 2005 - 16:51:55 EST

Best

Matthieu

An example:

> library(aod)
> data(dja)
> negbin(y ~ group + offset(log(trisk)), ~group, dja, fixpar = list(4, 0))

Negative-binomial model

negbin(formula = y ~ group + offset(log(trisk)), random = ~group,

data = dja, fixpar = list(4, 0))
Convergence was obtained after 113 iterations. Fixed-effect coefficients:

```            Estimate Std. Error z value Pr(> |z|)
(Intercept)  -0.5526     0.2277 -2.4267    0.0152
groupTREAT   -1.0205     0.2598 -3.9287    < 1e-4
Overdispersion coefficients:
Estimate Std. Error z value Pr(> z)
phi.groupCTRL   0.8287      0.412  2.0117  0.0221
Overdispersion coefficients set to fixed values:
Value
phi.groupTREAT     0
```

Log-likelihood = -121.149; nbpar = 3; df.residual = 72; Deviance = 111.826; AIC = 248.297

De: r-help-bounces@stat.math.ethz.ch de la part de Edward McNeil Date: jeu. 6/30/2005 8:50
À: r-help@r-project.org
Objet : [R] Dispersion parameter in Neg Bin GLM

Hi,
Can someone tell me if it is possible to set the dispersion parameter constant when fitting a negative binomial glm in R? I've looked at the documentation and can't find the appropriate argument to pass. In STATA I can type: nbreg depvar [indepvar...], offset(offset) dispersion(constant). Thank you

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