Assess prison effectiveness

Why is it so difficult to assess prison effectiveness? Each author attempted to prove that prison either worked or didnt work.

Please review all the 3 articles google the articles

1) Petrosino, A., Turpin-Petrosino, C. and Finckenauer (2000). “Well-Meaning Programs Can Have Harmful Effects! Lessons From Experiments of Programs Such as Scared Straight.” Crime and Delinquency 46: 354-379.

2) Sauders and Billante. Does Prison Work?

3) Lee, David & McCrary, Justin. The Deterrence Effect of Prison: Dynamic Theory and Evidence