The Guardian Education section has this article about the old proverb "You can't judge a book by its cover". According to recent research, apparently you can. Well, at least, 77% of the time you can.
Piters and Stokmans's unabashedly bookish study, called Genre Categorization and Its Effect on Preference for Fiction Books, was published just a few years ago, in the journal Empirical Studies of the Arts. Their experiment builds on a pilot study Piters conducted in the mid-1990s. There, he found evidence that a book cover "has to visually represent what the book is about since that might be an important cue in identifying a book as belonging to a specific genre".Of course, I couldn't help thinking, that's a pretty old proverb, and probably when it first started, book covers looked like this:-