That $.89/$1.00 female/male ratio looks like gross pay. For equal work, under equal conditions (same number of hours, same ratio of overtime/regular hours), the pay is identical.
At least, this is what the data shows for the Boston MBTA.
It makes me wonder and ask, “How many of these gender earnings studies confuse total annual take for pay rates?”
I have seen at least one study that says that in truth the average woman makes MORE per hour of work than the average man if you look at men and women who do the same kind of work.