Central Limit

why the bell curve keeps showing up

Take n random samples from the left distribution. Compute their average. Plot it on the right. Repeat. No matter what the source looks like, the averages form a bell curve. This is the central limit theorem — one of the most surprising results in mathematics.

Source Distribution
Distribution of Means (n=5)
click & drag on the source panel to draw your own distribution
5
1/frame
samples: 0
mean:
std:
The Cauchy distribution has no finite mean or variance. The central limit theorem requires finite variance to work. Watch what happens when that condition is violated — the averages never settle into a bell curve, no matter how many samples you take.
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