B. It is often said that the “gold standard” of social science research is to have a randomized experiment where some subjects are assigned to the “treatment” group while others are randomly assigned to the

“control” group. Here is an example: A school voucher program is limited to 1,000 voucher participants, but 2,000 families apply, with each having their child tested on a standard exam. The administrators of the program then randomly select 1,000 families that get the voucher—or the “treatment”—and treat the remaining 1,000 families as the “control” group. One year later, they test the children again and compare the change in average test scores of children from the two groups. They find that those who were randomly assigned to the “treatment” group have, on average, significantly higher test scores.