Definition
Plain language
How spread out a bunch of numbers are.
As stated in the literature
The expected squared deviation from the mean; 'variance explained' (R-squared) measures the fraction of observed spread accounted for by a fitted model.
Also called: variance explained
Why it matters: How much of the spread a model can explain tells you how much of what you are seeing is understood and how much is still unaccounted for.
For example, two classes can have the same average test score while one has everyone near 70 and the other has half at 40 and half at 100.
Heard on the show
“The aggregate average rises, the variance gets worse, and for any specific hard task, you might be worse off than just running sixteen attempts and crossing your fingers.”Episode 003 — How to Pick the Best of Sixteen Coding Agent Rollouts