I believe the research in question does not speak on the grounds such as to suggest women earn 20% less for the same job vis-a-vis men, but rather claims due to women are being under-represented in a variety of high-level jobs, on average, they earn less.

And the reason may not be in the realm of misogynist inclinations depicted at high levels of government, it may be the case on average women choose professions that pay less.

We know that men are more likely to go into “nerdy” professions such as math or engineering, whereas women are more likely to go into the caring professions and to spend more time looking after children [0].

0: Geary (2010); Halpern (2012); Maccoby and Jacklin (1974)