We know all about the Oprah effect on bestselling authors, but now it turns out there's also an Obama effect - on fashion and retailer stock prices.

We're talking about Michelle Obama, of course.

New York University finance professor David Yermack calculated that the First Lady created a whoppping $2.7 billion in value for the fashion and retail companies whose products she wore over 189 public appearances between November 2008 and December 2009, according to The Harvard Business Review.

While that's good news for companies like J. Crew - and their investors - the research notes that some of that came at the expense of other companies that lost market value in relation to her preferred designers.

The Harvard Business Review has the full details in nifty slide show form here.

For more images of the First Lady’s seemingly effortless style, click here.