If that 20% never had a factory job before, it is not a reliable indicator. It just means their current job is already shitty. They may get a factory job and realize that they were better off flipping burgers, even with less pay.
From TFA:
> When I first went to China as a naive 24 year old, I told my supplier I was going to “work a day in his factory!” I lasted 4 hours.