\begin{table}%T1
  \caption{Average parameters for different classes of sources proposed in this paper. For the classification criteria, see Sect.~\ref{analysis}.}
  \label{classes}
  %\centerline
 {\small
\begin{tabular}{l|rrrrrrrr}
  \hline
  \hline
Proposed   & $N$  & $z$ & $\nu_{\rm peak, OBS}$ & $\nu_{\rm peak, REST}$ $^1$ & $\alpha_{\rm below}$ &$\alpha_{\rm above}$ & Var$_{\Delta S}$ & Mode of $\nu_{{\rm Var}_{\Delta S,\rm MAX}}$\\
 class & Sources & & GHz & GHz  & & max & GHz\\ 
  \hline
gps & 29 & 0.59 & 2.77 & 3.86 & +0.91 & $-$0.88 & 1.21 & 36.7 \\
n   & 28 & 0.40 & 1.53 & 2.82 & +0.78 & $-$0.91 & 0.52 & 0.4\\
s   & 11 & 0.37 & 0.36 & 0.50  & --     & $-$0.84 & 0.78 & 4.3\\
f   &  7 & 1.07 & 2.01 & 4.54 & +0.36 & $-$0.34 & 1.50 & 4.3\\
f/s & 16 & 0.78 & 0.35 & 0.61 & +0.29  & $-$0.90 & 0.86 & 4.3\\
c   &  5 & 0.42 & 2.16 &  3.10 & +1.15 & $-$0.95 & 3.34 & 36.7\\
all & 96 & 0.58 & 1.65 & 2.77 & +0.82 & $-$0.86 & 1.04 & 4.3\\
  \hline
\end{tabular}
}
\smallskip
$^1$ Calculated when \textit{z} available;
gps = Gigahertz-peaked spectrum; 
n = Not enough data for GPS identification;
s = Steep spectrum;
f = Flat spectrum;
f/s = Flat at low frequencies, steep at high frequencies;
c = Convex (and variable) spectrum.
\end{table}