Section2.6posted

Section2.6posted - STOR 155, Section 2 Thur sday, Febr uar...

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Unformatted text preview: STOR 155, Section 2 Thur sday, Febr uar y 4, 2010 Section 2.6 Section 2.6: The Question of Causation Causation Common response Confounding Establishing causation Association does not imply causation! Some observed associations (all positive): Religious-ser vice attendance and longevity Year s of education and income SAT scor es and fir st-year college GPA Smoking and lung cancer Mar ital status and income (married men earn more) How much of each of these is explained by dir ect causation , and what else could explain them? Explaining associations Example 2.38 : x = mothers BMI (body mass index), y = daughters BMI . There is a positive association: r = +.507 , r 2 = 25.7% . Body mass is hereditary; daughters get half their genes from their mothers. So there is at least some dir ect causation . But this explains at most 25.7% of the variability in daughters BMI . The rest is due to other factors. Some possibilities for these other factors: We need to think about the how these other factors might affect daughters BMI , in order to understand the association more fully, and also in order to design further studies if necessary. A simple explanation (if we can establish it): Direct Causation. Changes in x are causing changes in y. Another simple explanation (if we can establish it): Common response. A lurking variable z is causing changes in both x and y . Explaining associations Dotted lines indicate associations to be explained....
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This note was uploaded on 06/12/2010 for the course STOR 155 taught by Professor Andrewb.nobel during the Spring '08 term at UNC.

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Section2.6posted - STOR 155, Section 2 Thur sday, Febr uar...

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