Talk show host Oprah Winfrey taped her farewell show yesterday at the United Center in Chicago. In front of 13,000 spectators (13,000!), a host of celebrities made surprise guest appearances, including Michael Jordan, Tom Cruise, Maya Angelou, Will Smith, and Madonna. (Also present was former California first lady and Oprah pal Maria Shriver, who took the opportunity to get in a jibe at her estranged husband Arnold Schwarzenegger.) For 25 years, Winfrey has been the most popular talk show host in the United States, and one of the most powerful women in the country. Most recently, many outlets credited her endorsement with helping propel Barack Obama to victory in the 2008 Democratic primaries (and the general election). Still, daytime talk shows are a declining medium: Just how big a difference did Winfrey really make?
In September 2008, economists Craig Garthwaite and Timothy Moore, of the University of Maryland, calculated Oprah's influence on the Democratic primary by comparing voting results in each county to subscriptions to Oprah's magazine, and sales of books recommended by Oprah. In the end, they found that a 10% change in circulation in a county correlated with a 0.2 percent increase in Obama's vote share. Extrapolated to the whole primary campaign, Garthwaite and Moore concluded that Oprah's endorsement was responsible for 1.015 million votes for Obama, "higher than the difference in votes between Obama and Hillary Clinton." With that kind of power over voters, it's probably a good thing Oprah's stepping down.