Dating a man 5 years younger
Meanwhile, US President Barack Obama, 48, and wife Michelle, 45, may have only a three-year difference in age but have been married for 17 years.
These people will have dates on a regular basis, and they may or may not be having sexual relations.
According to the study, the couples with the best chance are those where a woman with a superior education marries a man who is five or more years older than herself. By comparison, a marriage where a woman partners an equally poorly educated male divorcee who is five or more years her junior is up to five times more likely to fail.
The study is good news for David Cameron, 43, and wife Samantha, 38.
This period of courtship is sometimes seen as a precursor to engagement or marriage.
Dating as an institution is a relatively recent phenomenon which has mainly emerged in the last few centuries.
It can be a form of courtship that consists of social activities done by the couple.