Seems to me you are on the defensive and that you are not a fan of data and research. There are plenty of studies on wage gap.
Confidence is not the reason of the wage gap. Wages are based on negotiation power. That powers os based on many things, among them, your need for the job and the money (if you need the money you would take a worse job out of desperation). Also the other potential jobs you have on the line. That is why programmers make more money that waiters. Having said that, some employers didn’t like women. They think they are inferior and justify themselves with the “they migh get pregnant”. Notoriously, those employers have no problem with smokers or people who practice risk sports. Neither with people who binge drink. Why I’m saying this? Because those people usually have more absences that women, yes, even more absences than parents or maternity leave. That shows it is not about absences, is just an excuse.
Hell, I even have seen one recruiter discard a perfect profile for a position because “she might get pregnant and not return after maternity leave” and promote a guy who everyone knew that had another job lined up. For the record, the guy lasted a month, after that, the woman who was discarded was asked to make the job, without a rise or promotion. She eventually left too because she felt rightfully wronged. That is real life.
As you can imagine, we (the other women there) learned the lesson and also looked for other projects. Even today, that manager still thinks he was fair and didn’t discriminate. He didn’t understood why we left when he was “so happy with our work” and he “valued us so much”. Since he told us he was happy and give us praise for our work, he though rises and promotions weren’t needed, while the men, need those in order for them to be happy and felt recognized…
Since the companies know that other employers would discard perfectly capable women, they know they have less competence for hiring them and therefore offer less money. Since women have less offers, they have to settle for less. Less opportunities means lower wages.
In that context, asking for a rise is more risky for a woman. And look at this:
Even when women ask for a rise, that rise is denied. Why? Because many managers think that there is less risk of that woman leaving the company if they don’t get the rise.
In that regard I would advise to not bother to ask for a rise, but to look for another job and ask for more in the next job. Works better. But only people without dependants (like children) can afford to take the risk of changing jobs, so that is a limit.
Anyway, you can try to read some reasearch and data about this. Somethings are also useful for men.
