There are so many factors affecting this, not just the whole "Women earnt 79cent to every dollar a man earns" that's not the full extent.
In 2009, a group of economists studied thousands of business school graduates.
A year on after graduation the women earnt on average $115,000 whilst men earnt around $130,000 averaging a few more hours a week, with a bit more experiance prior to entering the workforce. Fair enough right?
9 years later, the same women were earning on average $250,000 whilst the mens average was $400,000. Thats a 60% difference. Now we have an issue, but how?
The highest paying jobs reward those who can work the longest and least flexible hours.
Which those whom have care giving responsibilities struggle with, which tend to be women.
In a speech, Claudia Goldin said: "The gender gap in pay would be considerably reduced and might even vanish if firms did not have an incentive to disproportionately reward individuals who worked long hours and worked particular hours."
Some jobs have large pay gaps, others have smaller. One study estimates that for lawyers, 1year out of the work force causes an 8.4% salary reduction. A HUGE difference.
The gap starts as small, gets larger through the 20's and 30's then shrinks again during a woman's 40's and 50's.
The reason? CHILDREN.
Having children makes it much harder to work to a specific schedual. Generally in the current economy jobs are 9-5, which worked great years ago when male workers had housewives to look after the children. Most women with young children do work now, but it's almost impossible to keep up with the hours of male counterparts.
Things have changed a little, but most things still point to women being primary caregivers.
Men are penalized more for having time away from work. Like the maternity and paternity gaps, but that's a conversation for another time. Companies tend to be more lenient with women's time off when it comes to kids. Certain hours in jobs are more important than others, and those tend to have higher salaries.
So, the responsibility still tends to lay with women to look after the kids when their sick, pickup and drop them off at school, and look after them as much as possible during school holidays.
Because of this, women find it harder to get into senior roles. The gap is significantly less for women without kids to women without kids.
To close the pay gap we need to make jobs work differently and be more flexible. Obviously this isn't possible for every role, but it would certainly make a difference. We need to tackle gender roles around parenting too.
There are many other causes, like direct pay discrimination, racial and disability bias, access to education and age, part time vs full time.
Sources and further reading;
@missy @rambo