popularity in right hand drop down menu

Can someone please tell me what algorithm "popularity" is based on? Is it how much a book or topic is checked out on my system? or in all of tinycat? or based on stars from amazon or goodreads? or some other criteria?
Thanks
Karen

>1 yedlint: Hi Karen! It's based on how many copies of the item have been cataloged on LibraryThing.

Let me know if you have other questions!

Zeph

>2 ZephCraven: Thanks