\begin{table}%t4
\caption{\label{tab:comp}Surveys comparing power-law spectrum indices of hard
X-ray loop-top and footpoint sources.}
%

%\centerline
{
\small\begin{tabular}{ccccccccccccccccc}
 \hline\hline
 & Time & Energy & Energy
 & \multicolumn{12}{c}{Power-law index ${\gamma}^{a}$} & \\
 \cline{5-16} Satellite & period & range & res. &
  \multicolumn{6}{c}{loop-top} & \multicolumn{6}{c}{footpoint} & Refs.$^{b}$ \\
 \cline{5-16} & [YY/MM] & [keV] & [keV] & N & Mn & Md & SD & K & S & N & Mn & Md & SD & K &
 S &  \\
  \hline
\textit{OSO-7} & 71/10--72/12 & 10--300 & $\sim$30 & 25 & 4.8 & 4.8 & 1.0 & --1.0 & 0.1 & 59 & 3.9 & 3.8 & 1.1 & --0.6 & 0.6 & (1) \\
\yohkoh & 91/10--96/05 & 14--33 & 10 & 25 & 8.2 & 8.1 & 1.5 & --1.1 & --0.1 & 16 & 7.3 & 7.7 & 1.3 & --0.9 & --0.4 & (2) \\
\yohkoh & 91/10--98/08 & 14--53 & 10--20 & 12$^{c}$ & 6.6 & 6.2 & 1.5 & 0.2 & 0.4 & 18$^{c}$ & 5.2 & 4.9 & 1.6 & --1.0 & 0.4 & (3) \\
\yohkoh & 91/10--98/08 & 14--93 & 10--40 & 5$^{c}$ & 5.5 & 5.3 & 1.3 & --1.5 & 0.2 & 13$^{c}$ & 4.3 & 4.1 & 1.0 & --1.0 & 0.7 & (3) \\
\yohkoh & 91/10--01/12 & 14--33 & 10 & 52 & 7.5 & 7.6 & 1.6 & --0.5 & --0.1 & 620 & 4.8 & 4.6 & 1.6 & --0.6 & 0.4 & (4) \\
\yohkoh & 91/10--01/12 & 23--53 & 10--20 & 23 & 6.7 & 6.9 & 1.4 & --0.7 & --0.2 & 338 & 4.0 & 3.8 & 1.1 & 2.1 & 1.0 & (4) \\
\yohkoh & 91/10--01/12 & 33--93 & 20--40 & 3 & -- & -- & -- & -- & -- & 155 & 3.4 & 3.4 & 0.7 & 1.2 & 0.6 & (4) \\
\yohkoh & 91/10-01/12 & 14--53 & 10--20 & 7$^{d}$ & 5.6 & 5.2 & 1.4 & --1.3 & 0.2 & 185$^{d}$ & 3.9 & 3.7 & 1.1 & 0.8 & 0.8 & (4) \\
\yohkoh & 91/10--01/12 & 23--93 & 10--40 & 1$^{d}$ & -- & -- & -- & -- & -- & 130$^{d}$ & 3.3 & 3.2 & 0.7 &1.4 & 0.6 & (4) \\
 \textit{RHESSI} & 02/02-05/07 & 3--1.7$\times10^4$ & 1--5 & 5$^{c}$ & 5.1 & 5.6 & 1.2 & --2.0 & --0.3 & 10$^{c}$ & 2.9 & 2.8 & 0.5 & --1.4 & 0.1 & (5) \\
 \textit{RHESSI} & 02/02--04/08 & 3--1.7$\times10^4$ & 1--5 & 50 & 5.4 & 5.5 & 1.2 & --0.8 & 0.3 & 0 & -- & -- & -- & -- & -- & (6) \\
 \textit{RHESSI} & 02/02--05/08 & 3--1.7$\times10^4$ & 1--5 & 0 & -- & -- & -- & -- & -- & 174$^{c}$ & 3.3 & 3.1 & 0.5 & 0.3 & 0.7 & (7) \\
 \hline
\end{tabular}}
\medskip
$^{a}$ N -- number of events; Mn -- mean, Md -- median, SD -- standard deviation, K --
 kurtosis; S -- skewness.\\
$^{b}$ (1) -- Roy \& Datlowe (\citeyear{r+d75}); (2) -- Mariska \& McTiernan
 (\citeyear{m+m99}); (3) -- Petrosian et~al. (\citeyear{pet02}); (4) -- this issue; (5) -- Battaglia \& Benz (\citeyear{b+b06}, \citeyear{b+b07}); (6) -- Krucker \& Lin
 (\citeyear{k+l08}); (7) -- Saint-Hilaire et~al. (\citeyear{k+l08}).\\
$^{c}$ Imaging spectroscopy.\\
$^{d}$ Events unbiased by the thermal component.
\end{table}