\begin{tabular}{lrrr}
\toprule
Continent & extracted studies & studies with usable estimates & usable estimates \\
\midrule
Europe & 83 & 48 & 2,868 \\
Asia & 77 & 47 & 1,746 \\
North America & 57 & 39 & 2,618 \\
South America & 8 & 5 & 177 \\
Africa & 6 & 4 & 133 \\
unknown & 6 & 0 & 0 \\
Oceania & 5 & 1 & 9 \\
\bottomrule
\end{tabular}