That is the main finding of a report, titled "Glass ceilings or Sticky Floors", by Alison Booth, Marco Francesconi and Jeff Frank, of the University of Essex. They claim that, on average, full-time women's wages are 17 per cent lower than men's and equal promotion opportunities don't close the gap.
The authors base their findings on a British Household Panel Survey between 1991 and 1995, and dismiss the popular view that women are promoted less than men because of a "glass ceiling" of covert discrimination. They even suggest women might have a slight edge in the promotion stakes because in that period full-time male workers had only a 9.2 per cent chance of promotion compared to 11.6 per cent for full-time women.
But at that point they believe discrimination against women takes its toll. Promoted men receive wages 20.4 per cent higher than unpromoted men, whereas promoted women gain wages only 9.8 per cent higher than unpromoted women.
It gets worse on the way up the career ladder. For otherwise identical men and women, if both experienced three promotions, a man would gain real wage growth of 32 per cent, while a woman would gain only 7 per cent. "We assume that there is discrimination in the sense that women in the post-promotion job are treated as being less productive than men, even though, objectively, their productivity is exactly the same," the authors stated.
"The guaranteed wage increase on promotion provides a comparable incentive to both women and men to train, and therefore there are comparable promotion rates. However, since the firm does not put the same value on women as men in the post-promotion job, it is less likely to match outside wage offers. As a result, promoted women receive lower wage increases over time than men."
Other findings are that both men and women are more likely to be promoted if they work longer hours, and professional and managerial workers are more likely to be promoted than unskilled workers.
Ms Booth said: " We use the term `sticky floors' to describe the situation where women are promoted and receive a wage increase, but then find it hard subsequently to gain higher wages. While some women can get through the `glass ceiling', they remain stuck to the promotion wage floor after that."
"Over 1991-95 men continued to gain from past promotions, while women did not. The dynamic effect of promotion on wage growth is therefore likely to exacerbate the already large gender gap in wages."