**Variance decomposition formula, conditional variance formulas** or **law of iterated variances** also known as **Eve's law**

EVPV(expected value of the process variance) + VHM (variance of the hypothetical means)

X의 변화에 따른 Y의 평균 변동성 + X를 알고도 남는 Y의 불확실성

XY 2차원 분포 생각하면 이해 편하다 - E[], V[] 결과가 상수가 아니라 함수로 나옴 적분위해

decomposes the variance of two random variables on the same probability space into "explained" and "unexplained" components

**Eve's law**, from the initials EV VE for "expectation of variance" and "variance of expectation".