DAVIS, Calif. ( TheStreet) -- Add Tiger Woods to the list of factors that need to be modeled into equity risk algorithms.

A new study from University of California, Davis finance professors estimates that shareholders of such Tiger Woods-endorsed stocks as Nike ( NKE) and PepsiCo ( PEP) -- which makes Gatorade -- have lost between $5 billion to $12 billion in market value since the Tiger sex scandal broke.

Not even the best golfing clinic could correct that hefty share price slice.

While much of the focus in the aftermath of Tiger's sexual bogey has focused on the massive hit to his unprecedented endorsement earnings, the UC Davis professors have quantified a loss to shareholders in these Tiger-endorsed stocks that would equate to decades' worth of Woods' personal endorsement income.

Victor Stango, a professor of economics at the UC Davis Graduate School of Management, and co-author of the study along with economics professor Christopher Knittel, looked at stock-market returns for the 13 trading days that fell between Nov. 27, the date of the car crash that ignited the Woods' scandal, and Dec. 17, a week after the golf great announced his indefinite leave from the sport.

The UC Davis economists compared returns for Woods' sponsors during this period to those of both the total stock market and of each sponsor's closest competitor. They also reviewed returns for four years before the car accident to determine how each sponsor's market performance normally correlates with that of the total market and of competitor firms.

In addition to PepsiCo and Nike, the study tracked the performance of seven additional publicly traded sponsors: Accenture ( ACN); American Express ( AXP); AT&T ( T); Electronic Arts ( ERTS); Procter & Gamble ( PG); TLC Vision ( TLCVQ); and News Corp. ( NWSA).

News Corp. owns Golf Digest; Gillette is owned by P&G; Electronic Arts offers the Tiger Woods PGA Tour Golf game.

Overall, the UC Davis study concluded that the scandal reduced shareholder value in the sponsor companies by 2.3%, or about $12 billion, a finding that the authors said cannot be explained away by typical daily variation in stock performance.

Not surprisingly, the three sports-related companies, Electronic Arts, Gatorade and Nike, fared the worst, experiencing a 4.3% scandal-generated drop in share value. That percentage drop equals a stock market handicap of $6 billion.

Accenture, one of the first companies to drop Tiger Woods -- and a company that is not sports-specific -- experienced no ill stock market effects from the scandal.

"Nike and other premier sports-related sponsors are special for an athlete like Tiger Woods," the UC Davis finance professors explained. "They are themselves powerful brands that add value to Tiger's brand and create other financial opportunities for him. This gives a premier sports sponsor the bargaining power to capture some of the profits generated by an endorsement deal with Woods -- so that if the Tiger brand is tarnished, those profits may decline."

While the pace of losses had slowed by Dec. 11 -- the day Woods announced his leave from golf -- the study found that by as late as Dec. 17 shareholders had yet to reverse their losses.

The UC Davis professors say that their study speaks to an important question for investors: Do celebrity endorsements present downside risk for equity shareholders?

"Our analysis makes clear that while having a celebrity of Tiger Woods' stature as an endorser has undeniable upside, the downside risk is substantial too," the authors concluded.

Maybe next on deck to be studied is not just downside risk from celebrity endorsements, but bankruptcy risk: TLC Vision Centers filed for bankruptcy in U.S. and Canadian courts on Monday.

-- Reported by Eric Rosenbaum in New York.

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