MEPX
Chapter 2 of 10All chapters
  1. 1What is one row
  2. 2Rates and denominators
  3. 3Beyond the average
  4. 4Compared with what
  5. 5Aggregation traps
  6. 6Noise and significance
  7. 7Metrics and proxies
  8. 8Missing data
  9. 9Reading forecasts
  10. 10A reading routine

Chapter 2 of 10

Rates and denominators

Out of how many.

Percentages need a base

A 40 percent rise from a tiny base is noise wearing a suit. Always find the underlying counts before reacting to a percentage.

  • Compare rates, not counts, when group sizes differ.
  • A percentage of a percentage is almost always misread.

Relative and absolute

A halving of risk sounds dramatic and may move one case in ten thousand. Both figures should be reported, and the absolute one is what affects decisions.