def icc_3_k_ci(alpha=0.05)
        per=1-(0.5*alpha)
        fl=icc_3_f.f.quo(Distribution::F.p_value(per, @df_bt, @df_residual))
        fu=icc_3_f.f*Distribution::F.p_value(per, @df_residual, @df_bt)
        [1-1.quo(fl),1-1.quo(fu)]