← The Green

The Commons Year · ages 15-18

Errata: Two Pools

The idea: a total can say the opposite of every group inside it when the groups are mixed differently; compare like with like before you rank.

Read it

Who is in this book

Every recurring character has a short tune, so you can tell who is on stage before a word is said. The tunes play only when you tap, and the Reading Access sound switch turns them off.

The Honest Page

Which parts of this story are true, stretched or made up?

True

  • Simpson's paradox is when a trend that appears in every group of data disappears or reverses when the groups are added together, usually because the groups are of very different sizes in the things being compared. Source
  • A well-known medical study compared two treatments for kidney stones. One treatment did better for small stones and for large stones, yet worse overall, because it had been used much more often on the harder, large-stone cases. Source
  • In the case, Riverside passed 50% of its beginners and 90% of its improvers, 60% overall; Hillside passed 40% of its beginners and 80% of its improvers, 70% overall.

Stretched

  • In the case, every swimmer is neatly either a beginner or an improver. What we simplified: Real clubs have swimmers of every level, and how good a club is depends on much more than one badge. Splitting into two groups shows the idea; a fair comparison might need more groups, and more than one measure.

Made up

  • The two swimming clubs, their badge records, the summer special, Sam, Mr Grant, Ms Osei and Mrs Lin are made up. Simpson's paradox is real.

Tara’s sentence

The case stops where Tara speaks. Write the sentence you would have said. It stays on this device.

Ring the hammer for someone

Pick this book for someone younger. The link carries only the book, and it will wait for them on the Green.

Across the Table → For the grown-up: the story in three lines, one question to ask, and one thing to do together.