Definition
Plain language
A measure of how closely two orderings of the same things agree.
As stated in the literature
Correlation computed on ranks rather than raw values (e.g. Spearman or Kendall tau); used here to test whether an ordering at year five predicts the final year-twenty ordering.
Also called: rank correlations
Why it matters: It answers whether an early standing predicts the final one, which tells you if a long test is really measuring anything the short version missed.
For example, if the top three finishers at the halfway point are still the top three at the end, the two orderings correlate strongly even if the point totals changed a lot.
Heard on the show
“They use a rank correlation called Kendall tau — and for our purposes the only thing to know is that it's a number between minus one and one, where high positive values mean two rankings line up well.”Episode 035 — Why Frontier Agents Ask for Clarification at Exactly the Wrong Moment