I am fairly new to GLMs, and am currently working with a quasipoisson distribution due to overdispersion. I have read through the relevant sections of Mixed Effects Models and Extensions in Ecology with R - however I am struggling to pin point just how I should be reporting these results?
I would like to state the amount of variance (variance or deviance?) that this model explains - do I need to calculate this just by (null deviance - residual deviance) / null deviance, OR should I be incorporating the dispersion parameter? ie: (null deviance - residual deviance) / (null deviance * SQRT(dispersion)). It is unclear to me which is correct, or if I should be doing something different all together.
Any help in interpreting this would be much appreciated!
I've included the output for this model for an example:
Call: glm(formula = PiecesTD ~ offset(LVolumeTD) + flocation + fMonth, family = quasipoisson, data = SA) Deviance Residuals: Min 1Q Median 3Q Max -4.1015 -1.1388 -0.2585 0.7566 4.6368 Coefficients: Estimate Std. Error t value Pr(>|t|) (Intercept) -2.0462 0.2196 -9.318 2.98e-12 *** flocationEG -0.8730 0.2202 -3.964 0.000249 *** fMonth6 0.7108 0.2512 2.830 0.006833 ** fMonth8 -0.1706 0.2783 -0.613 0.542760 --- Signif. codes: 0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1 (Dispersion parameter for quasipoisson family taken to be 3.281157) Null deviance: 262.45 on 50 degrees of freedom Residual deviance: 156.52 on 47 degrees of freedom AIC: NA Number of Fisher Scoring iterations: 5