The Non-Equivalent Groups Design (hereafter NEGD) is probably the most frequently used design in social research. It is structured like a pretest-posttest randomized experiment, but it lacks the key feature of the randomized designs -- random assignment. In the NEGD, we most often use intact groups that we think are similar as the treatment and control groups. In education, we might pick two comparable classrooms or schools. In community-based research, we might use two similar communities. We try to select groups that are as similar as possible so we can fairly compare the treated one with the comparison one. But we can never be sure the groups are comparable. Or, put another way, it's unlikely that the two groups would be as similar as they would if we assigned them through a random lottery. Because it's often likely that the groups are not equivalent, this designed was named the nonequivalent groups design to remind us.