Transparency is a wonderful thing but it has its limits. The problem lies in interpreting the thing disclosed. Take the new Equality Bill. Harriet Harman, the Minister for Women, has said that the Government will oblige private sector companies to publish figures showing their gender pay gap, as a way of shaming them into paying women more. It's a safe bet it'll turn out that, per capita, men get paid significantly more than women. Cue for Ms Harman to return to the Today programme to talk about glass ceilings.

She was eloquent yesterday, telling us that a part-time women worker is paid 40 per cent less than her full-time male equivalent. Movingly, she asked: “Do we think she is 40 per cent less intelligent, less committed, less hard-working, less qualified? It's not the case. It's entrenched discrimination.”

Well, no, if you put it like that. But try turning the matter round. If you compare that intelligent, hard-working woman, not with a full-time male equivalent, but a part-time male worker, you know what you find? She's paid more. In the year to April 2007, according to the Office for National Statistics, weekly median gross earnings for a woman working part-time are £145.60; for a man, £137.80. Is the part-time male less committed, less intelligent, etc? Dunno.

Of course, women's pay is less than men's overall. The ONS puts the gap, as measured by median hourly pay, excluding overtime, at 12.6 per cent. Weirdly, the difference was smallest in Northern Ireland, at 2.8 per cent. You never thought of Northern Ireland as a hotbed of feminism, did you?

But the real question is why. And it's not a bit clear that entrenched discrimination is the answer. Women may see lower pay as a reasonable trade-off for having more time to themselves - or, being women, for their children. They may, contrary to government policy, prefer to rear their own children, rather than farming them out to someone else.

The psychologist Susan Pinker asked, in a book titled The Sexual Paradox, and plainly designed to tease, “why females are biologically driven to nurture their young rather than climb the corporate ladder”. Why indeed? But it's a perfectly valid choice if some decide that the rat race isn't for them.

The really interesting comparison isn't between women and men but between single, childless women and men. If you compare women who aren't married or cohabiting with men who aren't married or cohabiting, you know what? The pay gap goes the other way. Hourly pay for the women is £8.82; for men £8.72. The moral is that if women want equal pay, they should give up men and children. Any takers?

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