By Martin Shankleman

Business correspondent, BBC news



Lesbians may have more motivation, say the researchers

The figures are derived from the official Labour Force Survey, which since 1996 has collected information on gay individuals who live together.

But the researchers who conducted the analysis say there is no clear cut explanations for the startling pay premium enjoyed by lesbians.

"Everybody speculates about that," says co-author Alan Marin of the London School of Economics.

"There are various possibilities, the most likely relates to child bearing.

"When employers consider recruiting for high-paying jobs they are less likely to hire women who tend to go off and have babies at inopportune moments."

More motivation?

The pay gap could also highlight the economic cost of childbirth in another way, he believes.

They might want to prove themselves as good as men, by working hard and being enthusiastic

Report co-author Dr Reza Arabsheibani

"It's known that women suffer a big fall off in pay, once they have children.

"This is to do with women who go into part time work, once they return, and they also tend to drop into less favourable occupations."

Another intriguing possibility is that homosexual women are more motivated to succeed in the work place.

Report co-author Dr Reza Arabsheibani, of Swansea University, speculates that lesbian women might even have a particular personality type.

"They might want to prove themselves as good as men, by working hard and being enthusiastic," he argues.

Greater control

Dr Arabsheibani also singles out another disadvantage for straight women who take time off for child-rearing - they miss out on update training, and their skills fall behind colleagues who stay at work.

"We know pay is positively related to formal education and learning on the job," he says.

"The discontinuity in their working life could have negative effect on the pay of women."

A more speculative explanation, advanced by one gay activist, related to the way gay women have children through IVF.

He felt this might give lesbians greater control over when they had children, and they could time childbirth to fit in with a lull in their, or their partner's, career.

More educated

But whatever the reasons, the effect is not just evident in the UK.

A similar pay premium is enjoyed by lesbians in the States, according to the authors, but not to the same extent.

In related work, they report that homosexual women in the USA also earn more than comparable straight women, although the gap is around 14%.

However the message for gay men is less encouraging, as the "gay pay effect" works in reverse, and they earn less than comparable straight men.

In the UK the pay gap is 1%, in the States researchers say the penalty is around 9%.

The research also highlights other differences in gay employment patterns.

In both the USA and UK same sex couples are on average younger and more highly educated than heterosexual couples.

And they tend to concentrate in selected areas, with a high share of same-sex couples in California, and London.