In his study on celebrity products, Craig Garthwaite reports that in the week following an Oprah endorsement, a selected title could experience a sales increase of up to 400 per cent. But in the 12 weeks following that, overall sales of adult fiction titles actually decreased by 2.5 per cent.
Sales of non-endorsed titles by book club authors also increased during that 12-week period, but romance, mystery, and adventure categories experienced significant decreases. Garthwaite speculates the decrease is “likely as a result of the endorsed books being more difficult than those that otherwise would have been purchased,” or as Mother Jones writer Kevin Jones joked: “While millions of Oprah fans were pretending to slog their way through Faulkner and Tolstoy, they were too drained to read their usual light fare. So the beach reading genres suffered.”
While Garthwaite’s theory is impossible to prove, he makes his case in a 49-page paper, available here as a PDF.