Associated Press
Oprah Winfrey

Having a novel endorsed by Oprah's Book Club is akin to winning the lottery for many authors. Indeed, Oprah's recommendations have turned obscure titles into bestsellers.

For example "Anna Karenina," Leo Tolstoy's tragic 19th-century love story, hit No. 1 on USA Today's Best-Selling Books list after Winfrey embraced it.

Similarly her endorsement of "Say You're Not One of Them," a collection of short stories by Uwem Akpan about Africa, boosted his book to No. 9 on USA Today's list. The publisher reports that there were just 77,000 copies of the novel in print when Winfrey selected it, so an additional 780,000 copies were reprinted to meet the demand, according to USA Today.

Now that her show is off the air, Oprah continues her book club via her website. However, new research suggests that Oprah's book club has done little to buoy literature or reading in the public at large.

While Winfrey's endorsements increased sales of favored titles, they caused a decrease in sales for the book industry as a whole, according to a 2012 study by Craig Garthwaite, an economist at the Kellogg School of Management. He found that on average in the 12 weeks following an endorsement, "weekly adult fiction book sales decreased by a statistically significant 2.5 percent."

Garthewaite postulates that this shrinkage occurs because Oprah's selections tend to be longer and more difficult classics that require more time and energy to read. As a consequence people reading Oprah's books don't buy their usual fare or quantity of books.