An instructor gave students the option to purchase an interactive program that allows them to answer questions during class and receive credit for participating. Alternatively, students could work an extra problem during weekly homework assignments. The instructor randomly selected 10 students, then randomly divided them into two groups of five each. One group was provided the interactive tool, the other group was asked to work the extra problem. The instructor knew from prior experience that the interactive tool increases attendance. The table displayed contains the final exam scores for the 10 students, on a scale from 0 to 100.