There's something in what he's saying - women don't get paid less due to sick-days as a result of menstruation, but they may get paid less and miss-out on promotions because employers are less keen on employing women because of women-specific issues such as maternity leave, and because if women take more sick days they're less favoured by employers.
Women do tend to suffer more problems as a result of their cycles, such as headaches and IBS, and the majority of women will suffer from dysmenorrhea at some point in their lives, which is defined as 'pain during menstruation that interferes with daily activities'. So women may in theory need more sick-days than men - effecting productivity, and in turn meaning employers are perhaps less likely to promote women due to how this effects their work or because too many sick-days adding up will see women more likely to face disciplinary action for sickness. This reminds me of the Australian Manufacturing Workers Union (AMWU) who wanted 12 days annual menstrual leave from Toyota in 2005 - they wanted additional days sickness to prevent women from facing disciplinary for women-specific monthly occurring illness out of their control, however if this had gone through it'd mean employers would be less likely to hire women.
Women who do take sick-days for menstrual problems shouldn't be shamed.
A couple of replies here seem to imply a sense of disapproval over women who do take sick-days for menstrual related problems, short of haemorrhage or ovarian tumour. I feel no guilt what-so-ever in having taken days off work due to menorrhagia, I'm sure my employers would have also preferred me at home on the odd occasion rather than bleeding all over the office, although granted I made up for the work I missed. Many menstrual problems are seen as 'part of being a woman' so many women will not know how to prevent them, or for some it may not be easy to prevent these problems, menstrual problems are just as real as any other health problem - why should women be expected to suffer?
IF menstrual problems do cause problems with productivity, what about other days of a woman's cycle?
Menstruation = reflective, so better at reviewing work.
Pre-ovulation = dynamic, so better at learning, clarity, concentration, researching, structural thinking, and better physical stamina.
Ovulation = expressive, so better at communication, productivity, and teamwork.
Pre-menstrual = creative, so can think more out-of-the-box, more assertive and better at problem solving.
Men may be more consistent throughout the month, however women are better emotionally and mentally equipped at different points in their cycle to do certain tasks thus potentially increasing their productivity. Many employers are currently looking into getting their female employers to share information about their cycles or sending them to cycle-specific lectures so that their female employers can work in such a way to take full advantage of the benefits of their cycle to improve office productivity.
Women shouldn't be discriminated against - I'm fairly certain Thompson is in agreement - but if women are taking more days off due to menstruation (or due to pregnancy/maternity leave) then of course this may be a contributing factor to why women are paid less.
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Bloodheart
Good-looking girls break hearts, and goodhearted girls mend them.