On a happier note, the 2006 equation identified two couples with a good chance to make it to their fifth anniversary, in 2010: Ben Affleck and Jennifer Garner, and Matt Damon and Luciana Barroso. Sure enough, they made it (and are still married).

As impressive as these results are, we believe even more scientific progress is possible. We have refined the equation by drawing on recent data as well as the research conducted by Garth in his fiendishly clever new book, “Brain Trust: 93 Top Scientists Reveal Lab-Tested Secrets to Surfing, Dating, Dieting, Gambling, Growing Man-Eating Plants, and More!”

While the 2006 equation did a good job over all of identifying which couples were most likely to divorce, some of the specific predictions proved too pessimistic. Because Demi was so famous — and much more famous than Ashton — we gave their marriage little chance of surviving a year, but they didn’t split until 2011. We were similarly bearish on Tom Cruise and Katie Holmes (because of his fame, his two failed marriages and their age gap), but they’re still together.

What went right with them — and wrong with our equation? Garth, a self-professed über-geek, has crunched the numbers and discovered a better way to gauge the toxic effects of celebrity. Whereas the old equation measured fame by counting the millions of Google hits, the new equation uses a ratio of two other measures: the number of mentions in The Times divided by mentions in The National Enquirer.

“This is a major improvement in the equation,” Garth says. “It turns out that overall fame doesn’t matter as much as the flavor of the fame. It’s tabloid fame that dooms you. Sure, Katie Holmes had about 160 Enquirer hits, but she had more than twice as many NYT hits. A high NYT/ENQ ratio also explains why Chelsea Clinton and Kate Middleton have better chances than the Kardashian sisters.”