Correlation and Causation

1. Correlation and Causation Part III – Causation

2. This video is designed to accompany pages 19-24 in Making Sense of Uncertainty Activities for Teaching Statistical Reasoning Van-Griner Publishing Company

3. Human Inference Point Two variables can be highly associated and no causal links exist at all. Human inferences from graphs and numbers that suggest association, or exhibit strong correlation, have to be made carefully.

4. So Said the CDC April 28, 2000 / 49(16);346-9 Alcohol Policy and Sexually Transmitted Disease Rates --- United States, 1981--1995 • higher beer taxes were associated with lower gonorrhea rates among young adults Gonorrhea Rates Amount of Beer Tax

5. The Big Leap April 28, 2000 / 49(16);346-9 Alcohol Policy and Sexually Transmitted Disease Rates --- United States, 1981--1995 • A beer tax increase of $0.20 per six-pack could reduce overall gonorrhea rates by 8.9%. • Implication of “cause and effect” from evidence only of association. Gonorrhea Rates Beer Tax • Always dangerous to do. This claim in particular was widely challenged - in part on disposable income arguments.

6. What do you think? Causation or Not? Student Grades LDL Levels Time Spent Studying Hours Exercised Life Expectancy at Birth Final Exam Score GNP per capita Quiz Average

7. Gender or Socialization? What do you see?

8. The Old Horse • Correlation does not imply causation. • Need to be able to discern the strength of the association and the credibility of any implied causation. • Not unlike a discussion of confounding, you need to be on the look out for a third variable that might be responsible for the association you see between the original two variables.

9. Diet Drink Dilemma Digital Bits Skeptic Skepticism. Critical thinking. Podcast. Community. • A study at the Utah Health Sciences center found that the more diet soda in a person’s diet, the more likely that person was to become overweight or obese. “After adjusting for age, sex and ethnicity, Williams found that regular soft drinks were no longer significantly linked to the incidence of becoming overweight or obese, but diet soft drinks were.” • The media will pick up a press release about this study and report that diet soda can make you fat….

10. Diet Drink Dilemma Digital Bits Skeptic Skepticism. Critical thinking. Podcast. Community. • Of the people that consume a lot of fast food, those that are starting to experience weight gain are more likely to choose diet soda than those that haven’t experienced weight gain. So, diet soda consumption is probably highly correlated with people who have a slowing metabolism and a habit of eating fast food. Perhaps, it is not the diet soda that is the problem, but the type of restaurant where large portions of diet soda often accompany the food.

11. Diet Drink Dilemma New study is wake-up call for diet soda drinkers. Ryan Jaslow / CBS News/ June 29, 2011, 10:09 AM • Researchers divided mice into two groups, one of which ate food laced with the popular sweetener aspartame. After three months, the mice eating aspartame-chow had higher blood sugar levels than the mice eating normal food. The authors said in a written statement their findings could "contribute to the associations observed between diet soda consumption and the risk of diabetes in humans." • "Artificial sweeteners could have the effect of triggering appetite but unlike regular sugars they don't deliver something that will squelch the appetite," Sharon Fowler, obesity researcher at UT Health Science Center at San Diego and a co-author on both of these studies, told the Daily Mail. She also said sweeteners could inhibit brain cells that make you feel full.

12. One-Sentence Reflection Association doesn’t imply causation because of other variables that may be influencing the relationships, but could be evidence of it.