Hello,
I am looking to fit a GEE ZINB model using proc nlmixed. I have turned to proc nlmixed as neither proc genmod or proc GEE can handle zero-inflated distributions for GEE analysis.
Following SAS sources, such as note 2 here , I believe I can set up the nlmixed statement correctly as needed. However, I am not sure how to specify clustering. In general, my code looks like:
proc nlmixed data = data; /* linear predictor for zero inflation */ eta_zero = a0; prob_zero = 1/(1 + exp(-eta_zero)); /* linear predictor for negative binomial */; eta_mean = b0 + b1*dTLN + b2*dNLLN + b3*dT; mean = exp(eta_mean + myoff); IF y= 0 THEN lglk = LOG(prob_zero + (1-prob_zero)*(1+(phi*mean))**(1/phi)); ELSE lglk = LOG(1-prob_zero) + y*LOG(phi*mean) - (y+(1/phi))*LOG(1+(phi*mean)) + lgamma(y+(1/phi)) - lgamma(1/phi) - lgamma(y+1); model y ~ general(lglk);
random ??? ; run;
I understand proc nlmixed can utilize a 'random' statement which can include a subject identifier, but I do not want to include any random effects (I am trying to avoid a linear mixed effects model). I would just like to account for clustering/correlation as a subject can provide more than one response. Note, the data is not a longitudinal study setup.
Is there a way to manipulate the random statement to allow for some correlation structure but not to estimate any random effects, setting up for interpretation as a GEE? Or is there another statement/line in nlmixed I can do this?
Thanks!
@StatDave Thanks for the insight. Are you saying there is a way to implement the model I would like in GLIMMIX?
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