Demystifying AI · Stage 3
Averages and spread
The mean adds the values and divides by how many there are: the mean of 2, 4 and 9 is 15 ÷ 3 = 5. Spread says how far values sit from the mean; squaring each distance and averaging gives the variance. Squaring stops positive and negative differences cancelling out, and makes big misses count extra.
Why it matters: The same average-of-squared-differences idea is how training measures a model's errors.
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A refresher on mean and variance, if needed.
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