The UK has a long running body of research looking at pay inequality between men and women. It looks in detail not only at salaries although that is what the headlines boil down to - but it looks in detail at occupational segregation, and the gender proportions at different levels of responsibility, and across different sectors.  It uses case studies to draw comparisons between men and women doing the same jobs, or like work, or work of equal value (as set out in the legislation).  

It's fine to say that less assertive men may not negotiate higher salaries as the more aggressive and dominant ones but the way it all averages out - in some sectors in the UK there is a 40% pay gap between men and women. How do you explain that?  The average is about 14%. That is not purely down to men on the whole being better at negotiating their contracts than women are. And in fairness should an individual's contract be down to how well that individual can negotiate it?  Because then it opens up for unfair practice and favouritism for each individual, not just within the groups we've been talking about.

For all to be fair, for all people, within genders and between genders, a systematic pay scale and grading and job evaluation methodology should be used.  So people who do similar jobs with the same levels of responsibility, should be paid the same for that.  What UK research shows is that even with these 'fair' pay systems there are still numerous examples of women being paid less than men who are doing the same jobs.

An example that is a hot potato right now is with local councils - cleaning staff are much more likely to be women, the bin collectors are more likely to be men.  It's widely established that the jobs are equivalent in terms of level of responsibility and it constitutes work of equal value - yet the bin collectors get paid significant enough sums more than the cleaners. So for all to be fair, the cleaners should be being paid the same or closer to the amount the bin collectors earn.  There's no question of trying to make more men be cleaners or more women be bin collectors but where it can be shown that the work is equivalent, they should be paid fairly.

I'm not trying to make you agree with me (extremely unlikely!) but to give an understanding of how I have come to my viewpoint and how the British system has developed the way it has.

Another thing to mention is that there is evidence of a pay gap for certain ethnicities compared to white people.  This can't be explained by a difference in educational attainment.  I don't think it could be reasonable to suggest that black people are less good at negotiating their contracts than white people so it leads us to wonder what could be the cause of a pay gap between black and (some) asian groups compared to white people.   There is much less research available on that to be able to discuss it in detail.  This is where the motivation for more research comes from - is this a real issue, is there a race pay gap and if yes what could be causing that?

There is very clear evidence of a disability pay gap too, again which is not explained by a difference in educational qualifications or level of experience and nor by things like sickness absence - when all those have been accounted for, there is still an unexplained factor as to why there is a pay gap and a significant different in employment rates between disabled and non-disabled people.  I think it's worth trying to get to the bottom of, not by making assumptions one way or the other but through robust research.