MEPX
Chapter 6 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 6 of 13

Describing the spread

Range, quartiles and standard deviation.

Why spread matters

Two datasets can share a mean and be nothing alike. Standard deviation measures typical distance from the mean, and quartiles split the data into four equal parts.

  • The interquartile range ignores extremes, which makes it robust.
  • A box plot shows the middle, the spread and the outliers in one picture.

Outliers

An outlier is either an error or the most interesting row in the table. Investigate before deleting, because removing inconvenient points is how analysis becomes fiction.