Newswise — If Oprah Winfrey's influence on Christmas gift choices is anywhere close to her impact on book sales as found by a new study, retailers are going to be wishing they had stocked more leather duffel bags and collapsible lipstick cases.

Those are two of the products the talk show mega-host highlighted in "Oprah's Favorite Things," her annual holiday gift ideas segment that follows the model of her highly successful book club, in which she recommended novels to her viewers.

A study being released Dec. 23 by Brigham Young University economists is the first to use quantitative methods to discern just how much a difference her taste in books, some of them many years old, made to readers. The results confirm the conventional wisdom that her endorsement dramatically increased individual book sales, but also suggest that her impact lasted longer than previously thought.

"Oprah's recommendations had a bigger impact on the sales of books than anything that we have previously seen in the literature, or seen since," said Richard Butler, professor of economics and lead author on the study, published in the new issue of the journal "Publishing Research Quarterly." "Not only did her picks rocket from obscurity, in most cases, to the top of the best-seller lists, but our statistical tests proved they generally had longer staying power on the lists than other best-selling books."

The idea for the study came when Butler was using data on book sales to demonstrate a concept in an undergraduate econometrics class and a student asked, "What about Oprah's books?" Intrigued, Butler found that individual book sales results are not publicly available, so he turned instead to bestseller lists. He settled on "USA Today's," which lists its top 150 titles each week, regardless of category or hardcover versus softcover status. Butler and his team examined the 45 non-children's titles Winfrey picked from the club's inception in 1996 until she announced in 2002 that she would change the program and pick only "classics."

"Only 11 of them had previously been on the best-seller list, and the top rank that any of them ever achieved, of those eleven, was 25th," Butler said. "Of the first eleven books that she picked, all of them went to the top four within the week that she recommended them."

Butler also noted that Oprah's more popular picks that were later released in paperback spent, on average, 6.5 weeks in the top 25, even though they had been on the best-seller list a year earlier as hardbacks.

Additional evidence of Oprah's impact came when the researchers compared the duration of each of her picks on the list with the duration other titles spent in the top 150.

"It's not just an overall average," Butler said. "We're comparing the short-term, median-term and long-term books, with Oprah's short-term, median-term and long-term books, and those are really distinct. Her average and below-average picks stayed on the list much longer than the average and below-average bestseller books."

The researchers conducted statistical tests to verify that their results were strictly correlated with the "Oprah effect" and not the product of chance or some other variables.

Butler and his team are currently working to solve other Oprah-related puzzles, such as the impact of her current program to recommend classics (initial indications are that it is similarly significant) and the quantitative impact her picks have on the number of books sold.

Butler was assisted on the study by two of his students who were undergraduates at the time -- Benjamin Cowan, now a graduate student at the University of Wisconsin, and Sebastian Nilsson, a BYU senior economics major.

"The effect was huge in that the books came from almost total anonymity to become a best seller," Nilsson said. "It was greater than I would expect."

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Publishing Research Quarterly