04-06-2017 09:47 PM
I am working on a cross-sectional study and I will be using the modified poisson regression analysis. My data has a cluster variable.
Thus, I am running the code showed below. However, I do not know what type of working correlation should I use. Independent is the default but not sure how to decide this. Any help would be appreciate it. Thanks.
proc genmod data=data
model y = x1 x2/dist=binomial link=log
04-10-2017 03:56 PM
The unstructured matrix (TYPE=UN) is the most general, allowing all pairs in the clusters to have separate correlations. However, it is also the most complex since it has the most correlations to estimate. As a result, using this structure often results in model fitting problems, particularly as the clusters get large. The QIC statistics can help to determine an appropriate structure as discussed in this note. But remember that the GEE method implemented by the REPEATED statement is robust to incorrect specification of the structure, so it is common to use fairly simple structures such as the independence (TYPE=IND) or exchangable (TYPE=EXCH) structures.
04-10-2017 09:27 PM