|
Hello all,
i am trying to do a poisson regression with an outcome being rate of
disease, and independent variables being agecode (categories of age),
region, and sex.
I am trying to figure out how to interpret whether there is evidence of
overdispersion: i was taught that this can be accomplished by
looking at the value/df from the criteria for assessing goodness of fit
output...the closer the value is to 1 the less the influence of
overdispersion.
when i run the following code, i get the following output..
proc genmod data=mening_poisson;
class agecode sex region;
model count=agecode sex region / offset=l_pop dist=poi link=log type3;
run;
Criteria For Assessing Goodness Of Fit
Criterion DF Value
Value/DF
Deviance 161 224.3462
1.3935
Scaled Deviance 161 224.3462
1.3935
Pearson Chi-Square 161 204.5569
1.2705
Scaled Pearson X2 161 204.5569
1.2705
Log Likelihood 843.6215
Is 1.39 considered close to 1 ? what is the cutpoint for what
determines overdispersion based on the value/df stat?
Thanks, nevin
| 
