backslashbox is too wide

I feel the first column in my longtable is too wide. Please see the figure below

My code is:

\begin{center}
\begin{longtable}{|c|c|c|c|c|c|}
\caption{Error rates for SVM and 100 random counts. \label{tab:2}}\\
\hline
\backslashbox{Concepts}{Train sizes} & 10 & 100 & 1000 & 10000 & 100000\\
\hline
1 & 0.49 (0.00) & 0.49 (0.00) & 0.47 (0.00) & 0.43 (0.00) & 0.33 (0.00)\\
\hline
\end{longtable}
\end{center}


I wonder if there is some way to reduce the width of the first column?

Thanks and regards!

EDIT:

As Hugo suggested, I tried to specify the width for the first column.

\begin{longtable}{|p{50pt}|c|c|c|c|c|}


But it appears messed up

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migrated from stackoverflow.comAug 1 '11 at 5:20

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I don't find the width of the first column too bad. If you start trying to narrow it, the text is going to be pushed close to the diagonal line. – Charles Stewart Apr 22 '10 at 6:51

Try

\backslashbox{Concepts\kern-1em}{\kern-1em Train sizes}


or

\backslashbox{Concepts\kern-2em}{\kern-2em Train sizes}


or

\backslashbox{Concepts\kern-3em}{\kern-3em Train sizes}

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Did you tried to set the size of the first column like this:

\begin{longtable}{|p{50pt}|c|c|c|c|c|}


Have never worked with this \backslashbox. But this is the way you normally resize the columns in a longtable. Maybe it works..

EDIT: Or another try:

\backslashbox[2cm]..

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Thanks, Hugo! As you suggested, I tried to specify the width for the first column. But it appears messed up. – Tim Apr 21 '10 at 23:20