What the unpublished data show is that female faculty members in physics have lower salaries compared to their equally qualified male colleagues. "The model says that if we have two people who are identical in every way, the woman will make, on average, 6 percent less than the man," said Susan White, assistant director of SRC, quoted in the Physics Today article. The National Academies' study also found that there were inequities between men and women. Massachusetts Institute of Technology astronomer Claude Canizares, who co-chaired the study, explained that while universities do not purposely discriminate against women and minorities, inequities nevertheless persist. According to the Physics Today article, other studies and observations support the data, with two key reasons for the gender gap disparity. First, women are less aggressive in their salary negotiations and also less likely to ask for a raise during their tenure at an institution. The second reason comes from the fact that men are overrepresented in some scientific fields, which introduces an implicit bias in university departments. m"Boys in the department give money to boys in the department,” said a senior researcher quoted anonymously in the Physics Today article. To close the pay gap, MIT Professor Emerita Nancy Hopkins suggests that senior female faculty members need to serve on the hiring, promotion and editorial boards that are positions of power at most universities. Efforts must also include male support to promote women and minorities in science. “It’s hard to break a glass ceiling by banging your head on it from below," Canizares said. "It’s easier to break it from above with a sledge hammer."