[Wasabista]

There are problems with measurement. In Canada, we have a government commission that tries to rank jobs according to value-added. Their recommendations are not binding in the private sector, but they suggest that clerk-typists add more value than, say, shipper-receivers. The problem is that shippers have to move boxes around, which nobody likes to do, so it tends to get done by men, and if you don't pay more you can't find them. So this is a situation where "women are paid less for similar jobs" when this is not the truth at all.

It's also true that men are more ready to ask for more money than women are. And the squeaky wheel gets the grease.