 Now, this was one small study by one neuroscientist. The economist John Cawley walked us through some of the other literature on celebrity endorsements. Craig Garthway at Northwestern's done a neat paper on the effect of an endorsement of your book by Oprah's Book Club and found that it led to a jump in sales, not just of the recommended book, but also of other books written by that same author. And interestingly, it didn't increase book sales. People didn't buy any more books. They just switched to buying the one Oprah recommended.