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# handout_2_6 - 2.6 The Question of Causation Often the goal...

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2.6 The Question of Causation Often the goal in a study is to establish that changes in the explanatory variable cause changes in the response variable. What constitutes good evidence of causation? What different types of links between x and y can explain an observed association between x and y ? dotted line→ association between x and y unbroken line→ cause-and-effect link between x and y Causation - “ x causes y Example #1 x = mother’s body mass index y = daughter’s body mass index

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Common Response The observed association between the variables x and y is explained by a lurking variable z . Both x and y change in response to changes in z . This common response creates an association even though there may be no direct causal link between x and y . Example #1 x = the student’s SAT score y = the student’s first-year college GPA z = ability Example #2 x = private health spending in a given year (\$ billions) y = goods imported in a given year (\$ billions) z = general economic conditions in a given year 2
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## This note was uploaded on 02/23/2011 for the course STAT 2700 taught by Professor Bill during the Spring '11 term at Adelphi.

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handout_2_6 - 2.6 The Question of Causation Often the goal...

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