def _aicc(model_results, nobs, add_constant):
    """Compute the corrected Akaike Information Criterion"""
    aic = model_results.aic
    df_model = model_results.df_model
    if add_constant:
        add_constant += 1
    return aic + 2.0 * df_model * (nobs / (nobs - df_model - 1.0) - 1.0)
