Hi all,

I’m trying to set-up a spike and slab prior. Below is the code and error message and it seems to be related to the a conflict with the lambda parameter. I’m pretty sure the code is correct for the spike and slab, but if you see something strange, your comments would be appreciated. (I realize there are easier ways to specify the modeling, but this code is for pedagogical purposes).

Thank you!!!

```
modelString = "
data {
int<lower=0> n;
vector [n] readscore;
vector [n] Female; vector [n] ESCS;
vector [n] METASUM; vector [n] PERFEED;
vector [n] JOYREAD; vector [n] MASTGOAL;
vector [n] ADAPTIVITY; vector [n] TEACHINT;
vector [n] SCREADDIFF; vector [n] SCREADCOMP;
}
parameters {
real alpha;
real beta1; real beta6;
real beta2; real beta7;
real beta3; real beta8;
real beta4; real beta9;
real beta5; real beta10;
real<lower=0> sigma;
real<lower=0,upper=1> pi;
int <lower=0,upper=1> lambda; // Needed for Spike and Slab
real<lower=0> spike; // Needed for Spike and Slab
real<lower=0> slab;
}
model {
real mu[n];
for (i in 1:n)
mu[i] = alpha + beta1*Female[i] + beta2*ESCS[i] + beta3*METASUM[i]
+ beta4*PERFEED[i] + beta5*JOYREAD[i] + beta6*MASTGOAL[i]
+ beta7*ADAPTIVITY[i] + beta8*TEACHINT[i]
+ beta9*SCREADDIFF[i] + beta10*SCREADCOMP[i] ;
// Spike and Slab Priors
sigma ~ cauchy(0,1);
lambda ~ bernoulli(.5);
spike ~ normal(0,0.001);
slab ~ normal(0,1);
alpha ~ normal(0,5));
beta1 ~ lambda*slab+(1-lambda*spike); beta6 ~ lambda*slab+(1-lambda*spike);
beta2 ~ lambda*slab+(1-lambda*spike); beta7 ~ lambda*slab+(1-lambda*spike);
beta3 ~ lambda*slab+(1-lambda*spike); beta8 ~ lambda*slab+(1-lambda*spike);
beta4 ~ lambda*slab+(1-lambda*spike); beta9 ~ lambda*slab+(1-lambda*spike);
beta5 ~ lambda*slab+(1-lambda*spike); beta10 ~ lambda*slab+(1-lambda*spike);
// Likelihood
readscore ~ normal(mu, sigma);
}
// For posterior predictive checking and loo cross-validation
generated quantities {
vector[n] readscore_rep;
vector[n] log_lik;
for (i in 1:n) {
readscore_rep[i] = normal_rng(alpha + beta1*Female[i] + beta2*ESCS[i] + beta3*METASUM[i]
+ beta4*PERFEED[i] + beta5*JOYREAD[i] + beta6*MASTGOAL[i]+ beta7*ADAPTIVITY[i] + beta8*TEACHINT[i]
+ beta9*SCREADDIFF[i] + beta10*SCREADCOMP[i], sigma);
log_lik[i] = normal_lpdf(readscore[i] | alpha + beta1*Female[i] + beta2*ESCS[i] + beta3*METASUM[i]
+ beta4*PERFEED[i] + beta5*JOYREAD[i] + beta6*MASTGOAL[i]+ beta7*ADAPTIVITY[i] + beta8*TEACHINT[i]
+ beta9*SCREADDIFF[i] + beta10*SCREADCOMP[i], sigma);
}
}
"
SYNTAX ERROR, MESSAGE(S) FROM PARSER:
Parameters or transformed parameters cannot be integer or integer array; found int variable declaration, name=lambda
error in 'model42434d456d7_6c6886eff1f4f4aa9f39f0d04f5eb52c' at line 21, column 32
-------------------------------------------------
19: real<lower=0> sigma;
20: real<lower=0,upper=1> pi;
21: int <lower=0,upper=1> lambda; // Needed for Spike and Slab
^
22: real<lower=0> spike; // Needed for Spike and Slab
-------------------------------------------------
Error in stanc(file = file, model_code = model_code, model_name = model_name, :
failed to parse Stan model '6c6886eff1f4f4aa9f39f0d04f5eb52c' due to the above error.
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Looking forward to your topic!
```