Hi @DomLimo (and welcome to the SAS Support Communities! :-))
So, you are missing the truncated Poisson and truncated negative binomial distributions in the list of probability distributions available in the PDF function? In this case you can create your own functions using PROC FCMP.
Example:
proc fcmp outlib=work.funcs.prob;
function pdf_trpoi(n,m);
return(if n>0 then pdf('poisson',n,m)/(1-exp(-m)) else 0);
endsub;
function pdf_trnegb(m,p,n);
return(if m>0 then pdf('negb',m,p,n)/(1-p**n) else 0);
endsub;
run;
options cmplib=work.funcs;
After submitting the above code, functions pdf_trpoi and pdf_trnegb are available which compute probabilities for the zero-truncated Poisson and zero-truncated negative binomial distribution, respectively. The arguments of these functions are the same as those of the PDF function for the corresponding non-truncated distributions.
Example:
%let lambda=2.5;
data trpoi;
do x=0 to 10;
p=pdf('poisson',x,&lambda);
tp=pdf_trpoi(x,&lambda);
output;
end;
label p="Poisson(&lambda)"
tp="zero-truncated Poisson(&lambda)";
run;
proc sgplot data=trpoi;
xaxis values=(0 to 10);
yaxis label='Probability';
scatter x=x y=p;
scatter x=x y=tp;
run;
Given that you're working with fairly specialized models (I am not familiar with), whereas the above calculations are comparably elementary, I'm not sure if this answers your question.
