Use the Following Information for Questions

Multiple Choice

Use the following information for questions:
In a report by AP, the headline read "Even light weekend use of the party drug Ecstasy might harm intelligence, a study suggests". The headline was based on a study of 28 Ecstasy users in their mid-20s recruited off the dance floor of a nightclub. The researchers compared this group with two others of the same size, age range, and education level - one consisting of drug-free people and another of people who smoked about as much marijuana as the Ecstasy group. The researchers reported weeks after partying, those who used Ecstasy along with marijuana performed worse on intelligence tests than people who just smoked marijuana or took no drugs at all.
-What was a potential confounding variable?

A) Drug use (Ecstasy, Marijuana only, or no drugs)
B) Score on Intelligence Tests
C) Educational Level
D) IQ (intelligence level) before taking drugs