Section 4.2.2 Causation

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Section 4.2.2Causation

• AP Statistics
• ww.toddfadoir.com/apstats

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The Question of Causation

• More than showing that variable x is associated
  to variable y most people are interested in the
  question does variable x cause variable y
• It is much more difficult to show causation than
  it is to show association.

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True Causation

• x Mothers body mass index
• y Daughters body mass index
• Body type is in part determined by heredity.
  Daughters inherit half their genes from their
  mothers. There is causation even though the
  mothers BMI explain 25.6 of the variation among
  the daughters BMI. (Page 233)

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True Causation

• x amounts of artificial sweetener saccharin in a
  rats diet
• y count of tumors in the rats bladders
• By putting rats into groups and feeding only one
  group saccharin, we can isolate the change the
  effect of the saccharin. Note a similar effect
  was not found in humans. (Page 233)

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Common Response
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Not Causation, Common Response

• x a high school senior SAT score
• y the students first-year college grades
• Even though there is a strong association between
  both variables, they are most likely responding
  to the common variables ability and knowledge.
  (Page 233)

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Confounding Variables
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Confounding Variables

• Two variables are confounded when their effects
  on a response variable cannot be distinguished
  from each other.

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Not Causation, Confounding Variables

• x whether a person regularly attends religious
  services
• y how long a person lives
• People who attend religious service do live
  longer, studies also show that they tend to take
  better care of themselves. They are less likely
  to smoke, more likely to exercise and less likely
  to be overweight (Page 234)

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Assignment

• Exercises 4.33-4.38, 4.41, 4.42, 4.43, 4.45,
  4.47
• Learner.org, Against All Odds Video on Causation