They're looking at geographically limited area, so there's no reason to expect a balanced gender ratio because men and women can move in or out at different rat

They're looking at geographically limited area, so there's no reason to expect a balanced gender ratio because men and women can move in or out at different rates. I'm guessing that previously a lot of single men moved there for economic opportunity but now both single men and single women are moving there for economic opportunity.