Confounding
Present students with studies that could benefit from an additional
control group.
Have students describe control groups that should be added. Alternatively, you could present them with an experiment that used several levels of an independent variable, but leave out one or more of the groups. Have students generate both the missing group(s) and the rationale for these groups.
Alternatively, you could use some humor and focus on the issue of confounding by using an exercise proposed by Michael Durnam.
- Obtain a copy of the western movie, The Guns of the Magnificent Seven.
- Ask the students if they can identify the confounding variable in this scene.
- Show a scene from the video that goes from approximately 13 minutes into the movie to about 19 minutes into the movie. ( In the scene, an individual, about to be hung for horse stealing, is allowed a "test" to see who is the true owner of the horse. Both "owners" line up on opposite sides of the street and start calling the horse. The horse gradually goes to the defendant (who doesn't own the horse) who happens to be standing next to a trough of water.
- Ask students to identify at least one confound.
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