Here’s something that no one ever explains. If American women earn 18.1 percent less than American men, as the OECD has just revealed, why does anyone employ men? If you had two similarly qualified applicants, one of whom was asking for a significantly higher salary, you’d hire the cheaper one, wouldn’t you?

Likewise, if having more female directors significantly boosts share performance, why do companies need to be told to appoint more female directors? Private firms are interested in profit, after all. If there is a large pool of undervalued women out there, surely, entrepreneurs will spot the opportunity.

We are going through an angry spasm about equal pay at the moment, and it is in the nature of angry spasms that accusation trumps accuracy. The focus on overall comparisons – not like-with-like comparisons, where men and women are doing the same job – followed the #MeToo movement and inherited its sense of burning injustice.

But is it really true to say that women are being systematically discriminated against in the workplace? In the United Kingdom, companies that employ more than 250 people are obliged to publish the average salaries of their male and female employees. A low-cost British airline called Easyjet turns out to have a gender pay gap — or, rather a #GenderPayGap, because these things are about letting the whole world know how you feel — of 51.7 percent.

Naturally, there was a great deal of huffing and puffing about that, not just on social media but also in mass media as well. How could any company pay its female employees only half of what their male counterparts were getting?

I’m sure, dear reader, that you guessed the explanation right away. Most of the cabin crew working for Easyjet – 69 percent – are women, whereas most of the pilots are men. The men who push the trolleys earn exactly what the women earn. The male and female pilots are likewise identically paid. (The idea that boys are on average likelier than girls to want to become pilots in the first place may be obvious to parents, but it is disallowed in our public discourse.)

Of course, if your primary motive is to advertise your left-wing virtue, you don’t care about numbers of pilots, and you will be outraged on principle at the idea of innate differences. Indeed, you’re happiest when you’re outraged. It’s not just that you dislike certain companies; it’s that you like disliking them.

What’s depressing, though, is the number of people who know that the statistics are tendentious, have some understanding of biology, and yet feel obliged to mouth the correct slogans in public.

Sure, there are individual cases of unfairness and misogyny – these things are in our fallen nature. But the pay gap is explained largely by other factors, notably the different choices that men and women tend to make about what hours to work, especially after they become parents.

Can we measure the impact of sexism on the pay gap? As a matter of fact, yes. Suppose we could find a company where people were paid blind – in other words, where their earnings were determined without any knowledge of their gender. Since sexism in pay would be impossible in such a company, any differential would be attributable to other causes.

As it happens, such a company exists. Uber drivers are paid according to time and distance by an algorithm that does not recognize their sex. According to a Stanford University study published a few weeks ago, female Uber drivers earn seven percent less than their male counterparts, largely because male drivers are prepared to work different hours, operate further from home, and drive faster. Since the pay gap between men and women doing the same job is, on average, a lot less than seven percent, it seems reasonable to infer that chauvinism is not the key factor.

What is really at stake here is the principle of free contract. If I want to work for you, and you want to hire me, and both of us are content with the terms, that should be no one else’s business. Sadly, we have moved a long way from that principle.

There was fury, for example, when it emerged that Claire Foy, who played Queen Elizabeth II in the Netflix drama, "The Crown," was paid less than Matt Smith, who played her on-screen husband. How, asked a hundred outraged pundits, could the Queen earn less than her consort?

Because, obviously, it was the rate their agents agreed to. In the same way, Marlon Brando got a much better rate for playing Superman’s dad than Christopher Reeve got for playing Superman. That’s how the market works. Is it so hard to grasp?