and, evelyn murphy says, bias can also play a role. >> the other way to look at the wage gap is that it is a proxy for power. the power of men in workplace over women. and so, as long as this wage gap exists, it is the signal and the measure of how unequal the power is within the workplace in america. >> thanks, anne. >> reporter: in 2013, the city of boston decided to tackle this inequity with programs for both employers and employees. >> by boston having equal pay for equal work, puts us on a competitive advantage. >> reporter: martin walsh is the mayor of boston. in 2015, his office launched an effort to train women to be better salary negotiators. >> we're actually challenging the status quo. >> reporter: the city teamed up with the american association of university women, a national advocacy group, to offer these free salary negotiation workshops. >> you know what you want. you know you're going to go for a higher number. >> reporter: they've trained more than 6,000 women so far. the goal is to train 85,000 by 2021, half the working women in boston. >> the biggest reason, it's