title: Step function for quasi poisson GLM
body: <p>I'm trying to fit quasi-poisson GLMs and GAMs using the step function to perform backwards selection. I used the following code but R returned an error as it couldn't calculate the AIC. The same model using a poisson distribution works but not quasi-poisson, is there any way to alter the function so it works?</p>
  
  <pre><code>full.mod03q&lt;-glm(Total.Positivo_2003~X.baix03 + Tot_PrevDesnut04
                   + Tot_HosDesid04 + Despesa_06 + prpnurb03 + prpnkid03
                   + dev03 + watertoilet03 + elec03 + dollpercap03
                   + abspov03 + gini03 + Importado.Outro.Municipio.Da.Uf_2003 
                   + Importado.Uf.Pais_2003 + elevation + floodplain + BIO1 
                   + BIO6 + BIO12 + deforestation_prop,
                   family="quasipoisson", offset=log(pop_2003), 
                   data=ama1@data)
  step(full.mod03q, direction="backward")
  </code></pre>