California has a new law: No more all-male boards
https://money.cnn.com/2018/09/30/news/california-requires-women-board-of-directors/index.html
It's dangerous to raise the minimum number of females on boards without accurate evidence. As is written on the article, it may potentially make unqualified females be members of the boards.
So, the number of the females on boards must be determined by the portion of female candidates.
Though it doesn't always reflect the number of qualified females, this system would be much more effective than defining the minimum number of female members without evidence.
