WikipediaOpenSecrets:
"Craig Garthwaite, co-author of a study on celebrity endorsements in the 2008 elections, told OpenSecrets Blog that Winfrey's endorsement of President Barack Obama was responsible for 1 million of his votes in the Democratic primary during the 2008 election cycle, giving him an edge over Hillary Clinton in the popular vote count.
The 'Oprah effect,' he said, was calculated by comparing Winfrey's magazine circulation in a county to the voter turnout in the same county. Other factors such as changes in sales of books selected by her book club were also taken into account."
