Women should be paid equally as well as men under the same vocation.
Assuming:
Two Job Candidates: M (Male) and F (Female)
The Vector of Employer Requirements [Degree, Experience,..] Is Equally Satisfied by Both Candidates
Employer Has a Ten Year Horizon
The Successful Candidate Will Stay for At-Least 10 Years with the Firm
On The Job Productivity is Equal For M and F
M and F Are Identical in ALL Respects apart from Gender. So Probability of Sickness etc is also the same. Hence we can cancel these effects out.
Over the Ten-Year Period:
(H Is a Measure of Productivity and is Equal for M and F)
(H1 Is Productivity in Year 1)
(H1M is Productivity in Year 1 for M)
Then,
H1M + H2M + H3M + H4M + H5M + H6M + H7M + H8M + H9M + H10M = Y
H1F + H2F + H3F + H4F + H5F + H6F + H7F + H8F + H9F + H10F = Y
H Increases over time as the worker gains skiils and expertise from working (on the job).
But. If F falls pregnant say during the 5th year, then:
H1F + H2F + H3F + H4F + 0 + H5F + H6F + H7F + H8F + H9F = V
(Assuming that F takes then entire fifth year off (doesn't affect analysis if this is shorter) and her skills set depreciates by 0%, then in the sixth year her productivity is H5F (not H6F))
Over the ten years then:
If F doesn't fall pregnant then Y = Y and the pay should be equal.
If F does fall pregnant then Y > V and so M should earn more.
Conclusion. If you want M and F to earn the same wage for an identical job etc then you need to enforce some sort of contract whereby F agrees that she will not fall pregnant during a certain period.
Also, adding in uncertainty where the employer is unsure about F falling pregnant in a certain period has its own losses therefore from the outset F should be offered a lower pay (unless you enforce a contract)
I know it sounds harsh but if you want equal pay then this is the only fair solution.
(May be some unintentional mistakes above)