He and another economics professor, Andrea Ichino analysed personnel data at an Italian bank which recorded the date and duration of every employee absence from work and found the absences of women below the age of 45 followed a 28-day cycle.
The professors concluded the menstrual cycle did increase female absenteeism and this explained at least 14 per cent of the gender pay difference.
More about the sick times:
in many Western countries women typically have more sick days than men of the same age - 7.6 more in Europe and 5.2 more in America and Canada.
"We think that biological difference could explain at least some of it.
"What we find is consistent with medical studies where women have turned in diaries of their conditions and their sickness and doctors find an incidence of PMS-related absences that is very consistent with our own estimate that came from the Italian data."
Perhaps good to keep in mind.
Moretti told Weekend Review the research was simply a small step in trying to say what the facts are and what the role of biology might be in women earning less - his guess is that child-rearing is a much bigger factor.
There is more in the article about starting a debate by tongue-in-cheek suggesting extra days off for women and more about what the state could do to address the pay-gap, but it seems to be one of those instances where ones rage is better suited for different topics....or so.