[Koha] sort by Popularity

[Howell, Lynda]

Can anyone explain the basis for the sort by "Popularity" in the Koha OPAC?  

Is it based on checkout frequency?  # of copies owned?  User ratings?  ...?

Thanks!

Lynda.

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Lynda Howell
Systems Librarian / Technologist
Union Institute & University
62 Ridge Street, Suite 2
Montpelier, Vermont 05602
(802) 828-8618
lynda.howell at myunion.edu