/* Macro for univariate zero truncated poisson model; Written by Zheng Sun */

%macro zero_trun_p(indata=,y=);
proc iml;
use &indata;
read all var{&y} into m;
mean=sum(m)/nrow(m);
diff=1;
initial=mean;
lambda_old=initial;
iters=0;
do while(diff>.0000005);
		lambda_new=lambda_old - (lambda_old - mean*(1-exp(-lambda_old)))/(1-mean*exp(-lambda_old));
		diff = abs(lambda_old - lambda_new);
		lambda_old = lambda_new;
		iters = iters + 1;
end;
mju_hat=lambda_new;
ods output mju_hat=mju_hat;
print mju_hat;
%mend zero_trun_p;