# Rstan: logistic regression

I am not sure how to use bernoulli_logit, I would like to fit a logistic regression model, but I am not sure is this model right?

infection ~ bernoulli_logit(b_0 + b_x* x[n]); // model

infection is the infection number, and my original formula is log(p/1-p) = b_0 + b_x* x, where p mean infection rate. So is this model right? because I cannot get the final result from this model, but there is no error comes out.

1 Like

That is the right idea, but it should probably be

``````infection ~ bernoulli_logit(b_0 + b_x * x);
``````

without the `[n]` index on the vector `x`. In any event, `b_0 + b_x * x` is assumed to be the log-odds of being infected for each observation.

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I think I should add [n], because I also have ‘for (n in 1:N)’

Well, in that case it should be

``````for (n in 1:N)
infection[n] ~ bernoulli_logit(b_0 + b_x * x[n]);
``````

but that is just a slow version of

``````infection ~ bernoulli_logit(b_0 + b_x * x);
``````

so you should do it the fast way.

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but it took 2 days, there is still no results, I am thinking, there should be sth wrong, it’s weird.

What is the whole Stan program?

ohh, the results came out, thanks :)