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Observational Studies and Experiments

Chapter 3 - Day 8 - Lesson 3.6

Learning Targets
  • Explain the concept of confounding and how it limits the ability to make cause-and-effect conclusions.

  • Explain the purpose of comparison in an experiment.

  • Describe the placebo effect and the purpose of blinding in an experiment.

Activity: Would you fall for that?
Answer Key:

When we were planning this course and had decided on starting each lesson with an activity, one of our main goals was to create a context for each concept so that students would retain what they had learned for longer.   Today we started by watching a video from Good Morning America (the full length version of the experiment is below).  The videoshows a social experiment in which the participants are told a beverage will actually make them immediately stronger.  Because the participants believed this, they actually did perform stronger on a carnival game, demonstrating the placebo effect.  The students thought this was so crazy that people actually believed this.  It was very memorable and a great way to introduce placebo effect and the need for control groups.


In order to cover the first and second learning targets, we gave students examples of poorly designed studies and asked them to identify the issues, similar to the activity yesterday.  The examples show the need for control groups and blinding.  They also give examples of confounding variables.

Teaching Tips

There is a lot of vocabulary this chapter.  Students did not struggle with conceptual understanding, but with all of the terms they had to keep straight.  Make students aware of this from day 1.  Take time in class to make flashcards each day or have students find another way to study.  We played a game in class that was a variation of the game Catchphrase.  We made a deck of notecards that had all of the vocab words and concepts from the chapter written, and the students played in groups according to the Catchphrase rules, which can be found here.

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