The Angelina Jolie effect (or how single women chase after married men)

As any single woman will tell you, all the good men are taken.

But that makes them all the more attractive, apparently.

Research shows that single women view married men as better catches than bachelors.

The fact that they already have someone's seal of approval adds to their desirability.

The phenomenon, known as 'mate poaching', could perhaps explain why Angelina Jolie fell for Brad Pitt, despite him being seemingly happily married to Jennifer Aniston.

Brad Pitt and then-wife Jennifer Aniston in 2004: But the marriage soon broke up

Did Angelina Jolie fall for Brad because of Jennifer?

The U.S. researchers showed 100 single and married female university students pictures of the same man and asked them how attractive they found him and whether they would try to start a romance with him.

In each case, the labelling on the photo had been tailored to suit what the volunteer liked in a man.

In addition, sometimes the man was described as single and other times he was said to be attached.

A group of men did the same with a picture of a woman.

The Oklahoma State University study found that the single men were most drawn to the woman when they thought she was single - but the reverse was true for the unattached women.

They, it transpired, had set their sights on the 'married' man. Four times as many of them were interested in him when they thought he was attached, as were keen on him as a singleton.

In contrast, married women were far more interested in the single man - suggesting they either respected the bonds of wedlock more, or yearned for a free spirit.

Writing in the Journal of Experimental Social Psychology, the researchers said: 'Single women in this study were significantly more interested in the man when he was attached.

'This may be because an attached man has demonstrated his ability to commit and in some ways his qualities have already been "pre-screened" by another woman.'

But men do not necessarily have the moral high ground.

Previous research has found that a man is more likely to try to lure a woman out of a relationship than a woman is to try to poach a married man.

The study also found that up to one in five longterm relationships begin when one or both partners are involved with someone else.