I am very new to SAS and need some help fitting a poisson model first, and in case of overdispersion, fitting a negative binomial mixed model for the following context: I want to isolate gender differences in the preferences for reports written by others using language that is high on several pre-determined categories (e.g., personal pronouns). I have raw counts of words in the report that fall into each of the various language categories as well as total number of words in the report. I understand that I have to use mixed Poisson/Negative binomial regression models as in my data - (1) I have multiple reports bought by the same person; and (2) the same report may be bought by multiple people; I also need to control for the random effects of two categorical variables: country and industry. How do I fit a mixed model for this situation with a count dependent variable (raw count of personal pronouns in the report), offset parameter (total number of words in the report), gender of the rater (m=0; f=1); and four nestings (raterID; reportID; countryCode; industryCode)? How do I know if Poisson or negative binomial mixed model fits better based on regression results? I understand that I need to use nlmixed. But I don't understand how to use it for my situation.I would really appreciate your kind help.
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