The researchers said their study suggests the older an over-40 groom is, the more likely it is that his bride is significantly younger, the San Jose (Calif.) Mercury News reported Wednesday.

The team said they were shocked to find the pattern unchanged by economic status.

"The poor guys marry down (in age) just as much as the rich guys do," said Paula England, a Stanford sociologist who co-authored the study. "That was kind of surprising to us."

England said brides of men in their 40s tended to be an average 7 years younger than their husbands, while women marrying men in their 50s were an average 11 years younger and brides of men in their 60s averaged 13 years younger than their beaus.

"We do find that money helps men's chances of getting married," England said. "But if we take youth as our crude measure of beauty, it doesn't seem like men are being able to exchange their money for younger women, so we don't know what's differentiating which older guys are able to marry very young women."