Ok. E’ una roba del genere:
Dopo aver combattuto con i pop-up di quell’orrido sito, rifiutato un paio di incredibili offerte e chiuso innumerevoli finestre, posso dirti come puoi fare.
`\documentclass[a4paper]{article}
\usepackage{array,booktabs,tabularx}
\begin{document}
\begin{table}
\caption{Definitions and Sources of Variables}\label{ematab}
\medskip
\begin{tabularx}{\columnwidth}
{>{\hsize=0.75\hsize}X
>{\hsize=1.50\hsize}X
>{\hsize=0.75\hsize}X}
\toprule
\textbf{Variable} & \textbf{Description} & \textbf{Source} \\
\midrule
nimp &
nominal import in dollars (for 1962–2000) &
Feenstra (2000) \\
Polity IV* &
inverse of “polity2'' indicator: $1={}$most democratic,
$21={}$most autocratic &
Gurr et al.\ (2003) \\
\bottomrule
\addlinespace
\multicolumn{3}{@{}l@{}}{\parbox{\columnwidth}{
* for these variables $i$ and $e$ indicate the values of an
importing and exporting country, respectively}}
\end{tabularx}
\end{table}
\end{document}`
Ciao
Enrico