An Urban Community Clinic Wants to Try a New Method

Multiple Choice

An urban community clinic wants to try a new method of getting drug addicts to kick their addiction. They advertise for participants in their lobby, and allow volunteers to choose to participate either in the treatment or control group. Three months later, they find that 65% of the volunteers are off drugs. This example illustrates the possibility of __________ as a plausible rival hypothesis.

A) history
B) maturation
C) regression artifact
D) selection