I worked in an office where there was a formal salary review done by external HR consultants.   It was done throughout the company. 

In my division, the only people identified as requiring salary adjustment upwards were female.   One of them held a PhD in a hard science.   Her pay was adjusted up more than 100%.   She didn't have children and had extensive experience in relevant areas.   Her next job (as she left the company not too long after learning just how badly she had been treated -- and lied to, by the way), she was in a role that paid, yet again, a lot more than the "adjusted" salary.

In my case, I was one of the most junior people at the firm, however, some of what I was doing was more involved than one would have expected for someone with credentials I had.   My salary was adjusted up about 75% AND the firm was ordered to pay salary retroactively for the period I had been doing that kind of work.

Who knows how it got this bad?  Bad HR?  Spineless executive leadership?