Correlation: Myths and Realities

1. Correlation: Myths and Realities Why Correlation is not Causation

2. What is Correlation? • correlation (often measured as a correlation coefficient,) indicates the strength and direction of a linear relationship between two random variables. • Variables are properties or characteristics of some event, object, or person that can take on different values or amounts.

3. How can you explain this? • People who often ate Frosted Flakes as children have ½ the cancer rate of those didn’t. • People who often ate oatmeal as children were 4 times more likely to have cancer than those who did not. What’s up?

4. How can you explain this? • People who had routine physicals in the previous 3 years were twice as likely to report high blood pressure and high cholesterol levels than those who did not. • How can this be explained?

5. How can you explain this? • A police chief in a small Midwestern town finds that as ice cream consumption increases, the crime rate also increases. It also decreases with a decrease in ice cream eating. Why?

6. How can you explain this? • The degree of obesity in children rises 2 percent for each hour of television viewed per week by those aged 12 to 17. • You probably see the simple answer, but can you delve deeper?

7. Last Questions • Why do children with bigger feet spell better? • Why do nations that have added fluoride to their water have a higher cancer rate? • Why, in certain counties in the southern U.S., are divorce rates negatively correlated with death rates?

8. What have you learned? • Correlation is not causation • Sometimes the correlation is dependent on a third (not easily seen) factor. 3. We need to be very careful when interpreting the results of data collection. You are now an official psychology genius!!!