Does menstruation explain gender gaps in work absenteeism?

"Ichino and Moretti (2009) find that menstruation may contribute to gender gaps in absenteeism and earnings, based on evidence that absences of young female Italian bank employees follow a 28-day cycle. We analyze absenteeism of teachers and find no evidence of increased female absenteeism on a 28-day cycle. We also show that the evidence of 28-day cycles in the Italian data is not robust to the correction of coding errors or small changes in specification. We show that five day workweeks can cause misleading group differences in absence hazards at multiples of 7, including 28 days"--National Bureau of Economic Research web site.