\begin{table}%t4
\caption{Comparison of the average $B$-band host galaxy properties$^{{a}}$.
\label{comparison}}
%\centerline
 {\begin{tabular}{lrccc}
\hline\hline
\noalign{\smallskip}
Name & $N$ & $\langle z\rangle$ & $\langle M_{B}(\rm host)\rangle $ & $\langle R_{\rm e}\rangle$ \\
& & & mag & kpc \\
(1) & (2) & (3) & (4) & (5) \\
\noalign{\smallskip}
\hline
\noalign{\smallskip}
BL Lacs (this work)        & 18 & $0.104\pm0.064$ & $-21.6\pm0.7$ & $7.6\pm3.2$  \\
Quasars \citep{jahn04}     & 12 & $0.094\pm0.043$ & $-20.9\pm0.7$ & $6.0\pm2.7$  \\
FR I RGs \citep{govo00}    & 17 & $0.069\pm0.031$ & $-22.1\pm0.6$ & $15.3\pm9.2$    \\
FR II RGs \citep{govo00}   &  6 & $0.050\pm0.016$ & $-21.9\pm0.6$ & $11.4\pm7.7$    \\
\noalign{\smallskip}
\hline
\end{tabular}}
\par
\smallskip
$^{{a}}$
Column (1) gives the sample; (2) the number of objects; (3) the average redshift; 
(4) the average host galaxy magnitude, and (5) the average effective radius ($\langle R_{\rm e}\rangle$ for RGs are in $R$-band).
\end{table}