\documentclass{article}
\begin{document}
\begin{table}
\small
\centering
\begin{tabular}{c|cc}
Source & Variation up (Stat. up) \% & Variation down (Stat. down) \% \\ \hline 
FSR-SingleTop\_SR2L & -1000.0 & 1000.0 \\ 
ISR-SingleTop\_SR2L & -1000.0 & 1000.0 \\ 
FSR-SingleTop\_tW2L\_CRtt & -3.6453 & -12.3989 \\ 
ISR-SingleTop\_tW2L\_CRtt & 4.6484 & -6.1217 \\ 
FSR-SingleTop\_tW2L\_CRttZ & -1000.0 & 1000.0 \\ 
ISR-SingleTop\_tW2L\_CRttZ & -1000.0 & 1000.0 \\ 
FSR-SingleTop\_tW2L\_CRWZ & -1000.0 & 1000.0 \\ 
ISR-SingleTop\_tW2L\_CRWZ & -1000.0 & 1000.0 \\ 
FSR-SingleTop\_tW2L\_VRtt & 10.4447 & -4.3586 \\ 
FSR-SingleTop\_tW2L\_VR3L & -1000.0 & 1000.0 \\ 
ISR-SingleTop\_tW2L\_VRtt & 4.2157 & -6.2761 \\ 
ISR-SingleTop\_tW2L\_VR3L & -1000.0 & 1000.0 \\ 
\end{tabular}
\end{table}
\end{document}
