If prison reformed criminals, illegal earnings once people were released ought to have gone down. But if prison was a “finishing school” for criminals, illegal earnings after serving time should have increased.
“Spending time in prison leads to increased criminal earnings,” Hutcherson says. “On average, a person can make roughly $11,000 more [illegally] from spending time in prison versus a person who does not spend time in prison.”
When Crime Pays: Prison Can Teach Some To Be Better Criminals : NPR
Personally, I think prison should be reformed so that criminals have very little free time. They should be working to better society, not just sitting around learning from other prisoners how to be better criminals upon release. The current prison system is hardly rehabilitation, and is definitely a waste of human resources.