Returns the simple predictive probability, averaged over each sample.

def simple_predictive_probability_multistate(M_c, X_L_list, X_D_list, Y, Q):
    """Returns the simple predictive probability, averaged over each sample."""
    logprobs = [float(simple_predictive_probability(M_c, X_L, X_D, Y, Q))
        for X_L, X_D in zip(X_L_list, X_D_list)]
    return logmeanexp(logprobs)