California is evaluating a new program to rehabilitate prisoners before their release; the object is to reduce the recidivism rate—the percentage who will be back in prison within two years of release. The program involves sev-

eral months of "boot camp"—military-style basic training with very strict discipline. Admission to the program is voluntary. According to a prison spokesman, "Those who complete boot camp are less likely to return to prison than other inmates."²⁵

(a) What is the treatment group in the prison spokesman's comparison?

the control group?

(b) Is the prison spokesman's comparison based on an observational study or a randomized controlled experiment?

(c) True or false: the data show that boot camp worked.

Explain your answers. plo47