MEPX
Chapter 8 of 13All chapters
  1. 1What analysis is for
  2. 2Types of data
  3. 3Collecting and sampling
  4. 4Cleaning data
  5. 5Describing the middle
  6. 6Describing the spread
  7. 7Choosing a chart
  8. 8Correlation
  9. 9Getting to causation
  10. 10Hypothesis testing
  11. 11Traps and paradoxes
  12. 12Tools of the trade
  13. 13Communicating results

Chapter 8 of 13

Correlation

Measuring how two things move together.

What the number says

A correlation runs from -1 to 1, where 0 means no linear relationship. It measures direction and tightness of a straight line pattern and nothing else.

  • A strong curve can have a correlation near zero, which is why you plot the data first.
  • Anscombe's quartet is four datasets with identical statistics and completely different shapes.

Not causation

Ice cream sales and drownings rise together because both rise with temperature. A third factor driving both is the usual explanation, and it is called a confounder.