Overall Notes

• There is one version of this assessment provided in the Teacher Resources Materials (TRM). Use this assessment as-is or use it as a model to create your own. 

• If you are making your own assessment, consider using the test bank and the ExamView software.

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Common Student Errors

• Student often have trouble explaining confounding variables. Be sure that the connect the confounding variable to the explanatory variable AND explain how the confounding variable could be causing changes in the response variable. 

• Sometimes students incorrectly believe that a control group has to get no treatment. Remember that a control group may be given an inactive treatment (placebo), an active treatment, or no treatment at all. 

• When students are describing a method to do random assignment using slips of paper, they often forget to mention “equal sized slips” and “shuffle the slips”. 

• When students are describing a method to do random assignment using technology, they often forget to mention “ignore repeats”. 

• When students are drawing an outline for an experiment, they often try to go directly from random assignment into the treatments. It is important for them to start with “Group 1” and “Group 2” before assigning treatments to remind them that random assignment creates roughly equivalent groups. 

• Students often confuse the purpose of random sample with the purpose of random assignment. We take a random sample so we can generalize to a larger population. We use random assignment so we can show causation.