Carrie Gracie's resignation as the BBC's China Editor has highlighted the issue of equal pay and it got us wondering how widespread the problem is in the UK.
Equal pay means staff doing the same job must be paid the same amount - it is a legal requirement.
Remember that having equal pay does not necessarily mean that you do not have a gender pay gap. The BBC reported in October that its gender pay gap was 9.3%, but that may be because more men are in senior jobs than women.
The chart above shows the number of cases about equal pay in employment tribunals that have reached conclusions.
What it does not show is the outcome of those cases. The Ministry of Justice publishes figures for the outcomes, but they are not as much help as you might expect.
Since 2011, so few cases were successful at a hearing they were recorded as 0%. But, on the flipside, the proportion of cases recorded as unsuccessful at a hearing was also 0%.
So what is going on?
A large proportion of cases are "dismissed upon withdrawal", in other words the employee and employer either came to a conclusion away from the tribunal or the employee withdrew, and in those circumstances the results are not made public.
So we don't know how often genuine cases of unequal pay occur.
No other area of complaint has this feature at tribunals - discrimination on the grounds of age or race or disability all have at least a small proportion of cases decided one way or the other by the tribunal.
It turns out that demonstrating that jobs are equal is such a difficult and drawn-out process that very few cases are ever decided at tribunal level.
"The procedures that have to be followed in equal pay cases are so complicated that people settle," said Caroline Underhill from Thompsons Solicitors.
"For all other claims the legal procedures are far less convoluted and the law is easier to understand."
It also means that cases which do proceed to tribunal can drag on.
"Equal pay cases are notorious for taking a long time... making the cases expensive", according to the TUC.
As we see in the chart at the beginning of this article there is no clear pattern in the numbers of equal pay cases being heard in tribunals.
And it is particularly difficult to read anything into it because of the impact of charging people who brought cases.
There was a big fall in the number of all types of cases going to tribunals when fees were introduced in July 2013.
The numbers went up again after July 2017, when the government was forced by the courts to stop charging fees.