I am talking about a population of criminals inside prisons, not about the general population.
It is impossible to measure with accuracy how much of a deterrent the death penalty is, since people will rarely answer a survey by saying: "I was planning to murder Joe Schmoe, but then I remebered the death penalty and thought better of it."
What you can measure with accuracy is the death penalty's main purpose: the elimination of recidivism among the executed. That's running at a 100% correlation.
How do we figure out which ones are "certain" to kill?
When they make the attempt they kind of send the message to us.
Obviously you are committed to your position on this, which is all well and good. But at the end of the day, you are contradicting both JP2 and B16's assertion that conditions necessitating the DP are virtually "non-existent". There must be some wisdom behind that statement. Shouldn't we try and discover what it is?