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Obsidian | Level 7 SBS
Obsidian | Level 7

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.  

Opal | Level 21

Unless you are looking at non-linear models, you should be looking at proc glimmix, it does support Poisson and negative binomial distributed responses with offset.

Obsidian | Level 7 SBS
Obsidian | Level 7

I tried the following code with GLIMMIX


proc glimmix data=myData method=quad;
class GenderRater RaterID;
model RAW_COUNT_PRONOUNS =GenderRater / link=log s dist=negbinomial offset=log_TOTAL_WORDS;
random int / subject=RaterID;


Within a second it gives the following error: The SAS system stopped processing this step because of insufficient memory


I just have 50,000 observations and 1500 Raters. What am I getting wrong?


Obsidian | Level 7 SBS
Obsidian | Level 7

I also tried NLMIXED and it gives no results, despite no error - 


proc nlmixed data=myData;
xb = b0 + b1*GenderRater + u;
mu = exp(xb +log_TOTAL_WORDS);
m = 1/alpha;
ll = lgamma(RAW_COUNT_PRONOUNS+m)-lgamma(RAW_COUNT_PRONOUNS+1)-lgamma(m)
model RAW_COUNT_PRONOUNS ~ general(ll);
random u ~ normal(0,s2u) subject=RaterID;


Obsidian | Level 7 SBS
Obsidian | Level 7

I was able to get NLMIXED running. The error was due to gender variable. It worked after dummy coding it. However, GLIMMIX still gives the same memory error.

Obsidian | Level 7 SBS
Obsidian | Level 7

Unfortunately, even the method=quad(fastquad qpoints=3) option gives the same memory error.



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