The Impact on Firm Valuation of Mandated Female Board Representation

  "We find that the constraint imposed by the quota
  caused a significant drop in the stock price at the
  announcement of the law and a large decline in
  Tobin’s Q over the following years, consistent with
  the idea that firms choose boards to maximize value."

The last word "value" in the abstract above is ambiguous; I guess the authors meant "share price". According to other non-monetary measures the "value" of the companies may have gone up. For example, a career path for women could keep them in the companies, making the entire Norwegian workforce more diverse.