When I first started to train as a psychologist, it was in the good old days of the late 1960s, when we were allowed to do punishment experiments on animals and people. They can't do it today, but we learned so much about how punishment works that I think by the late 1970s psychologists had just stopped doing experiments on it. There was no more to study. We knew when punishment worked and when it didn't work.
If you take psychology at a university today, you won't find a course on the psychology of punishment. The disappointing thing is that the criminal justice sector didn't pay attention to this research. Certainly the Americans in the late 1970s didn't pay attention to it, because if they had asked, any psychologist would have told them that more punishment, in whatever form--“scared straight”, boot camp--is not going to deter criminal behaviour. The evidence is just so crystal clear.
Now, after 30 years of experimentation in the United States, we have enough criminal justice studies--hundreds of them--to show that criminal sanctions do not deter crime.