(1) Women, when they do the same job or same type of work as men, get paid on average 77% less in their (i) hourly wages or (ii) weekly or yearly earnings (when they work the same amount of time), and (2) this hourly/weekly/annual wage gap is caused by a systemic, institutionalised, and misogynist wage discrimination against women in the West.Christina Hoff Sommers discusses this below.
First, one must distinguish between (1) full-time, annual earnings of men and women in vastly different professions and (2) the hourly wage for the same type of work.
If you take aggregated, averaged data on full-time, annual earnings, there is indeed a gender pay gap, but to prove that men and women are paid significantly differently for the same work in their hourly wage, you need to look at disaggregated data of hourly wages of men and women, not an average of lifetime earnings.
That is, you need to look specifically at men and women doing the same type of work, and then see if their hourly wages are different. When this is done, certainly some inequality can be found (and that is a problem), but the scale of this inequality is grossly exaggerated and women are generally paid the same wage for the same type of work as men do (see here).
Clearly the belief that there is some massive institutionalised, misogynist discrimination against women in the Western world is a myth.
The main reasons for the gap in average female full-time, yearly earnings as against earnings of men are (1) the different professions and career paths that women choose, and (2) different life choices of men and women.
If the difference between the full-time, lifetime earnings of men and women is regarded as an issue to be solved (and not, as some people argue, simply the result of the different career paths and life choices of men and women), then paid maternity leave and the encouragement of women into higher-earning professions could mostly fix it.
But what if after such measures a gap remains and it is because women freely choice different careers? Is this really a problem?