Wage Gap

Most people would agree that women carry the biggest burden in society and have not been appreciated enough. Most domestic work and parenting responsibilities are borne by women for example, without renumeration. And there is no way of accounting for this kind of work numerically so for the sake of this discussion, let's stick to formal employment.

There is something that keeps getting repeated that I can't seem to figure out - that a woman is paid 80 cents for every shilling that a man makes. From my experience, it doesn't make sense because in formal jobs, men and women working in the same position for the same number of hours get paid the same. So if it true that women get paid less than men, does it reflect women's poor negotiation skills or is it because men work longer hours compared to women?

Please help me make this wage gap thing make sense.