2_6_Handout - 2.6 The Question of Causation Often the goal...

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
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” EX #1 x= mother’s body mass index y= daughter’s body mass index A study of young girls measured their body mass index (BMI- a measure of weight relative to height) for both the girls and their mothers. The study also measured hours of TV, minutes of physical activity, and intake of several kinds of food. The strongest correlation (r= 0.506) was between the BMI of daughters and the BMI of their mothers. Body type is in part determined by heredity. There is therefore a direct causal link between the BMI of mothers and daughters. •Even when direct causation is present, it is rarely a complete explanation of an association between two variables. EX #2 x= amount of the artificial sweetener saccharin in a rat’s diet y= count of tumors in the rat’s bladder The best evidence of causation comes from experiments that actually change x while holding all other factors fixed. Experiments show that large amounts of saccharin (5% of diet) cause bladder tumors in rats. Studies of people who consume different amounts of saccharin fail to find an association
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 4

2_6_Handout - 2.6 The Question of Causation Often the goal...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online