1.1. Do you think the Oprah effect is likely to be similar to the endorsement effect of Theron or Harris? We are all familiar with celebrity endorsements: Neil Patrick Harris has been a long time endorser of Heineken Light, Charlize Theron is associated with Dior, while Rihanna sports Puma sneakers. But does this kind of image advertising really work? Do celebrity endorsements really increase sales of the endorsed good, and if so are new sales mostly at the expense of rival products or does this advertising increase sales in the category?

These are the kinds of questions analyzed by Craig Garthwaite, an economist at Northwestern. These are not easy questions to answer for some of the reasons of causality that we have described at various places in this book.