Lesson 2: What Is an Experiment?

Lesson 2: What is an Experiment?

Objective:

Students will learn about the elements of an experiment and the meaning of "causation". Students will learn to distinguish claims of causation from claims of association.

Materials:

Video: MythBusters’ Are Hands-Free Calls Really Safer While Driving?
https://www.youtube.com/watch?v=C-RAKWdKDEk

Note: If video is not found using link, please use a search engine (e.g., Google Video) and type "Mythbusters Are Hands-Free Calls Really Safer While Driving" to find it. The clip is a little over 9 minutes in length.

Vocabulary:

experiment subjects treatment treatment group control group random assignment outcome research question statistic

Essential Concepts:

Science is often concerned with the question "What causes things to happen?". To answer this, controlled experiments are required. Controlled experiments have several key features: (1) there is a treatment variable and a response variable, and we wish to see if the treatment causes a change that we can measure with the response variable; (2) There is a comparison/control group; (3) Subjects are assigned randomly to treatment or control (randomized assignment); (4) Subjects are not aware of which group they are in (a 'blind'). This may require the use of a placebo for those in the control group; and (5) those who measure the response variable do not know which group the subjects were in (if both 4 and 5 are satisfied, this is a 'double blind' experiment).

Lesson:

Display the following headlines to students:
1. Stop Global Warming: Become a Pirate
2. Lack of sleep may shrink your brain
3. Early language skills reduce preschool tantrums
4. Dogs walked by men are more aggressive
Discuss each headline by asking the following questions:
1. What is the headline implying with its wording? Answer: 1a is implying that you can stop global warming by becoming a pirate, 1b is implying that it’s possible to shrink your brain if you aren’t getting enough sleep, 1c is implying that having early language skills will decrease preschool tantrums, 1d is implying that dogs are more aggressive when they’ve been walked by men.
2. Is it implying causation or association? Answer: Discuss definitions of causation and association. Causation means there is a cause and effect relationship between variables. For example, heat causes water to boil; whereas association or correlation means that high values of one variable tend to be associated with high values of the other (or high values tend to be with low values). However, this is not necessarily cause-and-effect at play. For example, blanket sales in Canada are associated with brush fires in Australia - not because Canadian blankets cause the fires, but because Canadian winters cause blanket sales, and Canadian winters are Australian summers, which cause fires. 1a, 1c and 1d are implying causation and 1b is implying association.
3. How can you tell the difference between causation and correlation? What words stand out in these headlines? Answers will vary but some terms for causation include: cause, increase/ decrease, benefits, impacts, effect/ affect, etc.; and for correlation include: get, have, linked, more/ less, tied, connected, etc. In 1a, “become” stands out; in 1b, “may” stands out; in 1c, “reduce” stands out; in 1d, “are” stands out.
4. Change each causal version of a headline into a non-causal version and vice versa. Answers will vary but an example for 1a is to instead say Global Warming linked to increase of pirates.
Introduce the MythBusters video clip by answering the following questions, in teams, for their headline “Are Hands-Free Calls Really Safer While Driving?”
1. What is the headline implying with its wording? Answer: That hands-free calls might not be safer than holding a phone while driving.
2. Is it implying causation or correlation? How do you know? Answer: Causation because “really safer” implies that driving while on a hands-free call causes you to not drive safely.
3. How can we determine if this is true? Answer: Split the class into groups and have each team come up with a way to determine if this is true. Each group should assume that they get to examine 30 people.
Show the MythBusters video clip called Are Hands-Free Calls Really Safer While Driving? The clip can be found at:
https://www.youtube.com/watch?v=C-RAKWdKDEk
Focus students on the following guiding questions and ask them to take notes as they watch the video clip:
1. How did the MythBusters design the investigation? Answer: They conducted a driving test. In this case, one group is driving while on a hands-free call (because in the eyes of the law, this is no different than driving without being on a call). The treatment group is driving while on a hands-free call. They determined that "safe" meant passing the driving course by following the turn-by-turn navigation correctly and having no accidents. Passing the driving course was considered a "success".
2. What steps did they take? Abswer: They split the 30 subjects into two groups, 15 in one group and 15 in the treatment group, and had them drive a car in a simulator.
3. How is this different than your team’s headline responses in step 3 from above? Did the Mythbusters investigation match what you thought it would be about? Answers will vary depending on students' assumptions about the investigation prior to watching the video.
After viewing the clip, inform students that the MythBusters have just conducted an experiment, which is one method of data collection.
We begin with a brief introduction into “what is an experiment” but the definition will be developed over the next several lessons.
Guide students to identify the elements of an experiment by referring back to the video clip:
1. Research Question — the question to be answered by the experiment
  Are Hands-Free Calls Really Safer While Driving?
2. Subjects – people or objects that are participating in the experiment
  The 30 adults.
3. Treatment – the variable that is deliberately manipulated to investigate its influence on the outcome; this is sometimes known as the explanatory, or independent, variable
  Having drivers on a call without a cellphone in their hand. Using the research question as our guide, the question implies that we are experimenting with the hands-free calling, therefore that is the treatment as we are comparing it to hands-on calling.
4. Treatment group – the group of subjects that receive the treatment
  The 15 people who used the hands-free phone.
5. Control group – the group that does not receive a treatment
  The remaining 15 people who used the hands-on phone.
6. Random assignment – subjects are randomly assigned to either the treatment or control group
  It's unclear if random assignment was used in this video (if it was, we were not told so), but we're going to assume that people were randomly assigned to each group.
7. Outcome – the variable that the treatment is meant to influence; this is sometimes known as the response, or dependent, variable
  Success - whether or not a person was a safe driver by passing the test.
8. Statistic — a number such as a mean or proprtion used to summarize our findings for the control and treatment groups
  In this case, the MythBusters gave raw data. A statistuc would have been that 6.7% (1 out of 15) of the control group passed the test. Similarly, 6.7% of the treatment group passed the test.
Note: In this experiment, and in those found in the IDS curriculum, we use a treatment and a control group. However, a control group is not a necessary element of an experiment. Sometimes it is more appropriate to have two treatment groups with no control group (e.g., medical professionals testing different doses of drugs). The effect that is being studied will dictate whether to feature a control group or not.
Display the following questions on the board or projector. Using T-I-P-S, ask students to discuss them.
1. Why did the MythBusters follow all of these steps to design their experiment? Answer: In order to determine if driving while on a hands-free call was really safer than driving while holding a cellphone on a call.
2. We don't know how MythBusters chose who would be in the treatment group and who would be in the other group. Suppose that less-experienced drivers were assigned to one group and the more-experienced drivers ended up in the treatment group. Would you believe the conclusions? Answer: No, because less-experienced drivers would probably be more prone to mistakes (because they're inexperienced) than more-experienced drivers. Explain that this --another explanation for the cause-and-effect-- is called a confounding variable.
3. Explain that in order to make the two groups as similar as possible, experimenters usually assign subjects randomly. How might we randomly assign about half of the subjects to the treatment and half to the control? Answer: We might flip a coin, and those who get Heads go to Treatment.
4. Why would random assignment improve the MythBusters experiment? Answer: Because then the two groups would be more similar, so we wouldn't have a confounding variable to worry about.
Emphasize that without random assignment, we cannot determine causation because we are not comparing two similar groups.

Class Scribes:

One team of students will give a brief talk to discuss what they think the 3 most important topics of the day were.