Scientific research can be biased because those cosigning the research have something to gain. There have been plenty of so called research results passed around throughout history that have been totally fabricated.
Then you have to take into account that some organizations have not bothered to fact check before spreading research results because they are lazy.
I can see wage inequality existing in third world countries, but in the first world. No way. People are usually paid more based on value, overtime, et al. If you learn multiple languages you are almost guaranteed to make more working the same job for the same amount of hours. If you work overtime, you will make more than those who are clocking out on time.
That so called research about the gender pay gap doesn't bother to address different industries, education, job seniority, et al.
Some high money making industries are dominated by men because men choose to work in those industries and women don't.
Some college degrees are worth more than others and men tend to get the degrees that are worth more which will secure them jobs in money making industries.
Men tend to work overtime more than women.
These three factors alone guarantees that men will make more money in the work force than women. But if we're talking about a man and a woman working at the exact same job, with the same education, skills, seniority, and same working hours. They are both going home with the same paycheck.
No one is expecting a woman to get pregnant. If a woman chooses to have children she usually has access to maternity leave and daycare. But it is her own choice to get pregnant and she should expect that both men and women at her job have surpassed her and could be making more money by the time she returns to work. That's hardly inequality. Unless you think a person should be able to take a six month to a year break and return making just as much as those who worked their way to a higher pay check since the time of their absence.