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Slika - Shrani.si

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A. Juriˇ<strong>si</strong>ć in V. Batagelj: Verjetnostni račun in statistika 234<br />

✬<br />

Kovarianca<br />

Kovarianca Cov(X, Y ) slučajnih spremenljivk X in Y je določena z<br />

izrazom<br />

Cov(X, Y ) = E (X − EX)(Y − EY ) = EXY − EXEY<br />

Velja: Cov(X, Y ) = Cov(Y, X) (<strong>si</strong>metričnost) in<br />

Cov(aX + bY, Z) = a Cov(X, Z) + b Cov(Y, Z) (bilinearnost).<br />

Če obstajata DX in DY , obstaja tudi Cov(X, Y ) in velja<br />

Enakost velja natanko takrat, ko je<br />

z verjetnostjo 1.<br />

|Cov(X, Y )| ≤ √ DXDY = σXσY.<br />

Y − EY = ± σY<br />

(X − EX)<br />

σX<br />

Spremenljivki X in Y sta nekorelirani natanko takrat, ko je Cov(X, Y ) = 0.<br />

✫<br />

Univerza v Ljubljani ▲<br />

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☛ ✖<br />

✩<br />

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