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Slika - Shrani.si

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A. Juriˇ<strong>si</strong>ć in V. Batagelj: Verjetnostni račun in statistika 317<br />

✬<br />

. . . Vzorčno povprečje<br />

Oglejmo <strong>si</strong> vzorčno povprečje, določeno z zvezo<br />

X = X1 + · · · + Xn<br />

n<br />

ki je tudi slučajna spremenljivka. Tedaj je<br />

DX = 1<br />

n 2<br />

EX = 1<br />

n<br />

= 1<br />

n<br />

n<br />

Xi,<br />

i=1<br />

n<br />

EXi = µ<br />

i=1<br />

pada z naraˇsčanjem velikosti vzorca, tj. X → µ;<br />

(enako nam zagotavlja tudi krepki zakon velikih ˇstevil).<br />

✫<br />

n<br />

i=1<br />

DXi = 1<br />

n 2<br />

n<br />

i=1<br />

σ 2 = σ2<br />

n<br />

Iz druge zveze vidimo, da standardna napaka σX = σ √ n statistike X<br />

Univerza v Ljubljani ▲<br />

❙ ▲<br />

▲<br />

● ❙ ▲<br />

▲<br />

☛ ✖<br />

▲<br />

✩<br />

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