To test the value of the study guide, Professor Lewis gives a free copy to the students sitting in the first two rows of class. Later she finds that these students got better grades than the students in the back of the room (who didn't get study guides) . What is wrong with this experiment?

A) lack of an independent variable
B) confusion of experimentation with correlation
C) lack of random assignment to groups
D) lack of a dependent variable

Question

Camille Blandin · Accepted Answer

Final Answer : C, Explanation :  The lack of random assignment to groups means that there could be other variables (such as motivation or intelligence levels) that are causing the difference in grades between the two groups, rather than just the study guide itself. Without random assignment, the experiment cannot definitively show that the study guide is the cause of the better grades.

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