1\begin{tabular}{lrrr}2\toprule3Continent & extracted studies & studies with usable estimates & usable estimates \\4\midrule5Europe & 83 & 48 & 2,868 \\6Asia & 77 & 47 & 1,746 \\7North America & 57 & 39 & 2,618 \\8South America & 8 & 5 & 177 \\9Africa & 6 & 4 & 133 \\10unknown & 6 & 0 & 0 \\11Oceania & 5 & 1 & 9 \\12\bottomrule13\end{tabular}14