R help - Jun 2012 - Chi square value of anova(binomialglmnull, binomglmmod, test="Chisq")

Hi all,

I have done a backward stepwise selection on a full binomial GLM where the
response variable is gender.
At the end of the selection I have found one model with only one explanatory
variable (cohort, factor variable with 10 levels).

I want to test the significance of the variable "cohort" that, I
believe, is
the same as the significance of this selected model:
> anova(mod4,update(mod4,~.-cohort),test="Chisq")
Analysis of Deviance Table

Model 1: site ~ cohort
Model 2: site ~ 1
  Resid. Df Resid. Dev Df Deviance P(>|Chi|)    
1       993     1283.7                          
2      1002     1368.2 -9  -84.554 2.002e-14 ***
---
Signif. codes:  0 ?***? 0.001 ?**? 0.01 ?*? 0.05 ?.? 0.1 ? ? 1 

My question is:
When I report this result, I would say /"cohorts were unevenly distributed
between sites ( Chi2=84.5, df=9, p < 0.001)"/, is that correct? is the
Chi2
value the difference of deviance between model with cohort effect and null
model?

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On Jun 4, 2012, at 7:00 AM, lincoln wrote:
> Hi all,
>
> I have done a backward stepwise selection on a full binomial GLM  
> where the
> response variable is gender.
> At the end of the selection I have found one model with only one  
> explanatory
> variable (cohort, factor variable with 10 levels).
>
> I want to test the significance of the variable "cohort" that, I
> believe, is
> the same as the significance of this selected model:
>
>> anova(mod4,update(mod4,~.-cohort),test="Chisq")
> Analysis of Deviance Table
>
> Model 1: site ~ cohort
> Model 2: site ~ 1
>  Resid. Df Resid. Dev Df Deviance P(>|Chi|)
> 1       993     1283.7
> 2      1002     1368.2 -9  -84.554 2.002e-14 ***
> ---
> Signif. codes:  0 ?***? 0.001 ?**? 0.01 ?*? 0.05 ?.? 0.1 ? ? 1
>
> My question is:
> When I report this result, I would say /"cohorts were unevenly  
> distributed
> between sites ( Chi2=84.5, df=9, p < 0.001)"/, is that correct? is
> the Chi2
> value the difference of deviance between model with cohort effect  
> and null
> model?
I thought you said the response variable was gender? It seems to be  
'site' in these two models. Maybe you should give us some more  
information about how you constructed 'mod4'?

-- 

David Winsemius, MD
West Hartford, CT