A Half Century of Randomized Experiments on Crime and Justice.

Source: (2006) Crime and Justice. 34:55.

The number of randomized experiments on crime and justice with a minimum of 100 participants more than doubled between 1957 and 1981, when there were thirty-seven, and between 1982 and 2004, when there were eighty-five. There was
an increase in very large, multisite replication experiments and in experiments
in which the unit of randomization was the area. Results in the second period
were generally more encouraging, showing that some interventions reduced
offending. The main advantage of a randomized experiment is its high internal
validity. Randomization ensures that the average person or place in one
condition is equivalent on all measured and unmeasured variables to the average
in another condition, within the limits of statistical fluctuation. Observed
differences in outcomes can be attributed to differences in interventions rather
than to pre-existing differences. Randomized experiments have formidable
practical and ethical problems but are often feasible and should be used to test
causal hypotheses and evaluate well-defined technologies wherever possible. (author’s abstract)