Want your marriage to last longer? Then choose a wife who is five years younger to you and from the same cultural background, suggest experts from the Geneva School of Business. They claim this formula increases the chances of having a long and happy marriage by a fifth.

One couple that seems to fit the criteria is the Queen and Duke of Edinburgh. At 83, the Queen is four years and 10 months younger than the Duke and they share the same Royal background as Philip was a member of both the Greek and Danish royal families. Of the 1,074 couples looked at aged between 19 and 75, the report concluded that the wife should be 27 per cent more intelligent than her husband, hold a degree while he should not.

However, marrying a divorcee reduced the chance of marital bliss. "If people follow these guidelines in choosing their partners they can increase their chances of a happy, long marriage by up to 20 per cent," the dailymail.co.uk quoted lead researcher Nguyen Vi Cao as saying. Another study has revealed that married couples are their happiest two years, 11 months and eight days after tying the knot.

The research team asked 4,000 spouses to pinpoint their happiness during married life and calculated the time period when wedded bliss began. The study showed that just under three years was the time when couples feel completely comfortable with each other's bad habits and have a clear plan for their future.

The couples enjoy a full and active sex life and have carried out enough DIY for their house to feel homely and still find time for romantic meals together. "Three years after walking down the aisle and everything seems to come together - making each other laugh the most and cuddle up in front of the TV," said Carol Richardson of wedding website www.confetti.co.uk that carried out the research.

"They'll also spend the longest amount of quality time together each evening and make small gestures like offering to cook dinner and help with the washing up. "But there's no reason why you can't have a long and happy marriage if you stick to the guidelines our study also revealed. We're found the secret to the happiest time together isn't about big, expensive and lavish gifts but being there for each other to share special moments."

The study also found they enjoy their best sex, romantic meals and nights out with mates partying after two years and four months. Wives are likely to receive a respectable number of flowers, chocolates and compliments two-and-a-half years into their marriage.