sasmcmc

Understanding some parts of the implementation proc mcmc


I am studying one implementation of MCMC in SAS here https://support.sas.com/documentation/cdl/en/statug/67523/HTML/default/viewer.htm#statug_mcmc_examples13.htm

It implements

proc mcmc data=seeds outpost=postout seed=332786 nmc=20000;
   ods select PostSumInt;
   parms beta0 0 beta1 0 beta2 0 beta3 0 s2 1;
   prior s2 ~ igamma(0.01, s=0.01);
   prior beta: ~ general(0);
   w = beta0 + beta1*seed + beta2*extract + beta3*seed*extract;
   random delta ~ normal(w, var=s2) subject=ind;
   pi = logistic(delta);
   model r ~ binomial(n = n, p = pi);
run;

I fail to understand what are the purposes of the codeline ods select PostSumInt; and declaration parms beta0 0 beta1 0 beta2 0 beta3 0 s2 1; i.e. beta0 0? Are they starting values?

Also there seems to no definition of priors for beta coefficients, but I see there is one general definition prior beta: ~ general(0); How beta here is linked to beta0, beta1 etc and what is general(0)?

I really appreciate for any clarification on above codes.


Solution

  • In order of your questions:

    It's not super straightforward to search, but the SAS documentation explains all of this.