How does the system calculate a similarity index? I called up the profile of someone who posted and was surprised to see a SI of 37%. The person is alleged an 18-year-old male with Science Fiction/Fantasy on his bookshelf and strange fantasy and horror on his WL. I am 48 and have cozies, chidk lit and young adult literature on both my bookshelf and WL. It's very odd.

I have no idea but I've often wondered.  I came up with a 98% similarity on one account.  The member had 8 books on her shelf and they were all self-help books with one mystery.  I'm a mystery/thriller gal with contemporary fiction and history on the side.  Weird.

If I remember correctly, it's based on your WL books and books you've rated.  After they finished tweaking everything, I was at least 30% similar to everyone I came across, even if their WL was nothing like mine!  That seems a little weird to me, too.  The highest similarity ranking I have is about 50%.

Actually, I think it is just a "nice" thing, maybe to get you to look at someone's shelf.  I've been rated as high as 42% similarity with people who have books on a WL that I wouldn't even consider reading!  And to be honest, my lists would not interest them even one iota, either.  This is because I like historical fiction and maybe they are entirely into erotica, romance or vampires, or sci-fi!  How do you match that up!?!   LOL      D.