Suppose We Wish to Know If Long Prison Sentences Reduce

Multiple Choice

Suppose we wish to know if long prison sentences reduce the probability of recidivism. The basic model is
Repeat crime_i=B₀+B₁SentenceLength_i+e_i
Where repeat crime is 1 for released prisoners who end up being sent back to jail after release. Which of the following is viable as an instrumental variable?

A) A variable indicating the severity of the initial crime.
B) A variable indicating that the person had been randomly assigned to a judge with a record of harsh sentencing.
C) A variable indicating that the person had been randomly assigned to an educational program while in prison.
D) A variable indicating whether the person was a high school dropout.