The following research studies consist of two or more groups of scores being compared. For each, decide whether the study is experimental or non experimental, and then identify the dependent, independent, or quasi-independent variables.

A researcher in a medical school would like to test the effectiveness of different insomnia treatments. She conducts a study on 120 volunteers, who are randomly assigned to five different insomnia treatment groups, one of which is a control group receiving a placebo. The number of hours slept per night is recorded for each participant over 2 weeks.

This study is an example of an experimental study.

The type of insomnia treatment is the variable. The number of hours slept per night over 2 weeks is the variable.

Researchers at a medical school conducted a study to test the effectiveness of a new drug for lowering cholesterol. The 52 subjects who volunteered for the study were each given a randomly generated number. Subjects with an odd number were given the new drug, while those with an even number were given a placebo. Cholesterol levels before and after the treatment were measured for each subject, and the differences were computed.

This study is an example of study. The difference in cholesterol level is the variable. The treatment with drug or placebo is the independent variable.