Unofficial LibriVox Reading Group discussion

I'm curious how y'all decide how to rate books here -- share your approach?

I've been rating books in a paper book journal 1-20 for years, and at the moment am using the following conversion table:

    17-20 = 5*
    16 = 4*
    13-15 = 3*
    9-12 = 2*
    1-8 = 1*

However, looking at the ratings for books I've enjoyed recently, they seem to be averaging rather higher, so my rating is bringing the total down, even where I quite enjoyed it (the bulk of my reading is 3*.) Not sure what to do (if anything) about this.

I've never thought about rating by a numbers system. I just go by fair/good/better/best. If I think a book is bad, I don't finish it so don't rate it. Years ago I would trudge my way through a book, no matter how awful I thought it was. I finally decided that there are too many good books and no time to spend on the bad ones.