If you're the betting kind, an equation that predicts the longevity of celebrity unions -- and, unlike those couplings, has a pretty good success rate -- could actually put some money in your pocket.

New York Times writers John Tierney and Garth Sundem came up with the theorem in 2006. It takes into account the ages and relative fame of each half of the celebrity pair, how long they've been together, their marital history, and the sex-symbol factor, which was determined by looking at the woman’s first five Google returns and seeing how many depicted her in various states of undress.

Now that the writers have had a few years to test out the accuracy of their equation -- which they've dubbed the Sundem/Tierney Unified Celebrity Theory -- they're reporting it works quite nicely.

For example, it correctly predicted a short shelf-life for Demi Moore and Ashton Kutcher, Pamela Anderson and Kid Rock, and Britney Spears and Kevin Federline. (But really, did anyone need a fancy system to figure that out?) It also said the Ben Affleck/Jennifer Garner and Matt Damon/Luciana Barroso marriages would make it past their five-year anniversaries in 2010, and indeed they did.

Still, though, there were flaws. Since Demi was so much more famous than Ashton in 2006, the writers thought the pair wouldn't last a year — yet they survived far longer. The Sundem/Tierney Unified Celebrity Theory also thought the age gap between Tom Cruise and Katie Holmes, plus his fame and two previous divorces, spelled doom for the couple. But thus far, they've kept divorce lawyers at bay.

So some tweaks have been made. For example, while the old system measured fame by counting Google returns, the new equation instead counts mentions in the New York Times and divides that number by mentions in The National Enquirer. Using that method could reveal why the Cruise/Holmes union has stood the test of time: Katie Holmes had about 160 Enquirer hits, but she had more than twice as many NYT hits.

“It turns out that overall fame doesn’t matter as much as the flavor of the fame. It’s tabloid fame that dooms you," Garth explained. "A high NYT/ENQ ratio also explains why Chelsea Clinton and Kate Middleton have better chances than the Kardashian sisters.”

It probably also helps that Chelsea and Kate don't routinely make out with paparazzi cameras -- but what do we know? We're just casual observers without any numerical data on our side.

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