This function is a generic that is used to match the functions used with ppc_bars to calculate
the posterior predictive distribution of the data given the model.
id_post_pred(object, ...)A fitted idealstan object
All other parameters passed on to the underlying function.
posterior_predict methods should return a \(D\) by \(N\)
matrix, where \(D\) is the number of draws from the posterior predictive
distribution and \(N\) is the number of data points being predicted per
draw.