From a New York Times business section article about how job applicants and employers negotiate about pay:
At a time when most policies aimed at helping parents, especially women — like paid parental leave and child care support — are stalling out or facing resistance, the bans on salary history have been far less controversial, often garnering bipartisan support, said Andrea Johnson, who has pushed for these laws through her work at the National Women's Law Center...
The bans are still so new that it's hard to really judge how much has changed. Massachusetts's law, the first in the country, went into effect in 2018. There is some preliminary research showing that pay for women who change jobs has increased slightly in states with the bans. But other research shows less promising results.
"Before these laws were passed, women were underrepresented in high-wage jobs. That didn't change," said Ethan Rouen, a professor at Harvard Business School, who looked at data in one state that passed a ban and wound up not publishing his research because he didn't see any significant change.
"Wound up not publishing his research because he didn't see any significant change" is a non-rare outcome in both social science and scientific research, but it is a problematic one, because the non-publication deprives the public and policymakers of potentially useful information. If the newly passed law didn't really change anything, maybe knowing that would make other states hesitate before passing similar laws. Social science research has a bias toward publishing results that show effects, and toward not publishing results with "null effects." That, in turn, may give the public a misguided confidence that passing laws solves problems rather than just making politicians feel good while imposing compliance burdens and possibly unintended consequences on businesses and the general public.