'The O Factor' - Oprah's vote is just the business for Obama

They call it "The O Factor". When Oprah Winfrey, the American chat show host, media mogul and one of the richest women in the world, puts her name behind a product millions of dollars of sales are sure to follow. But can "The O Factor" do the same for a would-be President of the United States?

Once a year Oprah reveals her so called "favourite things", a shopping list of products that she claims are indispensable. Sales immediately soar for all the stuff she tips.

Shares in American kitchen wares shop Williams Sonoma, which had several items on this year's list, went through the roof after Oprah revealed she liked its plastic bowls and fairy cakes. So too did shares of Decker, the maker of Ugg Boots which also featured on her list. And it's not just small household items and fashion accessories that get the Oprah thumbs-up.

A $4000 (£2000) LG fridge freezer with built in TV and internet was included on this year's list, sending sales of the product flying.

Books chosen by the famous Oprah's Book Club also get a massive fillip once earmarked by the chat show host. A recent survey estimated that a mention by Oprah reaps an average of $80 million in extra sales for an author and that the book is guaranteed to remain on bestseller lists for months.

Josh Groban, a middle-of-the-road singer who used to have a fairly small following, released an album called Awake in October 2006 to fairly mixed reviews and very poor sales. Then came The O Factor.

Groban appeared on Oprah singing an old Christmas carol and sales of his album, which were at about 220,000 for the 13 months since release, shot up by 745,000 in five days. What is more his Christmas record, Noel, has sold 2.8 million and is set to be the biggest album of the year.

But now Oprah has moved into politics for the first time. Before Oprah announced her "favourite things" list this year she revealed that Barack Obama, the Democrat senator for Illinois and hopeful Presidential candidate, was her "favourite person" in the 2008 race for the White House.

In December, the media mogul took to the stage at an Obama rally in Iowa and thousands turned out to see her. The Democrat hopeful even joked that Winfrey could become the next Vice President, which drew a massive cheer before he added: "But you realise that would be a demotion."

So could Winfrey really swing the Democratic race? To realise what effect her endorsement might have in America, it is worth looking at the sheer reach of her business empire. Her TV show is watched by more than eight million viewers daily, her magazine and website have two million readers a month, and her newsletter has 420,000 weekly fans. Her empire will reportedly earn $260 million this year - and, on top of that, she runs three charitable foundations, with assets of over $200 million.

Forbes estimates Winfrey is worth a total of $1.5 billion, making her the richest African-American and the wealthiest entertainer. As Obama doubtless knows, her track record in business suggests she usually picks a winner. In comparison, author JK Rowling is second on the entertainment list with $1 billion and rival lifestyle queen Martha Stewart is third with $638 million - although the latter's homeware and magazine business was hit by her spell in jail for lying to investigators in an insider share dealing probe.

The Pew Research Center, a Washington think tank that tracks people in the news and their influence, is so intrigued by Oprah's unprecedented support of Obama for the Democratic nomination that it asked thousands of Americans whether they thought her backing would effect the outcome of the election. Sixty per cent of Americans believed Oprah's support would have a positive impact on Obama's campaign. But 69% said her endorsement would not affect their voting choice.

In past elections celebrity endorsement has rarely had a big impact. In fact only Richard Nixon, who got a massive surge after John Wayne urged his fans to vote for him in 1968, can truly be said to have benefited from the help of a star.

David King, a lecturer on public policy at Harvard, said: "In a crowded primary field, endorsements matter the most, and both the Democratic and Republican fields are very crowded now. If [an endorsement] could make any difference, it would make one now."

But Hillary Clinton still holds a commanding lead over Obama in the polls, and the primaries are days away. So if there really is something to be said for "The O Factor" in politics, now is the time for Oprah and Obama to prove it.