 there'd never been anything like that in the history of book recommendations at least in modern history and it wasn't just an endorsement it was a call to action to everybody go buy this book what do we know about the more general state of endorsement let's say lebron james is endorsing nike what do we know about the power of that type of endorsement where there's some affiliation but not necessarily a call to action it's a great question i don't have a good answer for you