# Variance: one idea, many roles

Connect squared deviations to volatility, risk forecasts, diversification, factor models, PCA, overfitting and variance swaps.

Fifteen interactive steps connect one identity across mathematics, quantitative finance and machine learning, with paced Coach–Zon narration.

Canonical page: https://21ifm.com/quant/mathematics/variance-one-idea-many-roles

## Explore

- [Mathematics for finance](https://21ifm.com/quant/mathematics)
- [Why variance estimates are noisy](https://21ifm.com/ml/why-one-week-of-risk-is-so-noisy)