Women are absent more due to their "monthlies"...and thus, pay gap.
I was going to say something absolutely tasteless and offensive here, but I think I will forgo such childishness. The person posting the article makes much better arguments compared to the PMS theory. And, seriously, I haven't seen many women around here skipping work because they forgot where Midol or Tampax are sold.
Also interesting is
Menstruation's connection to women bidding less competitively. What I want to know is if they've checked out any of these theories against post-menopausal women. And comparing women on the birth control pill or patch (which really kicks up hormone levels) to ones not adjusting their hormones. It would make for an interesting comparison.