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Slika - Shrani.si

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A. Juriˇ<strong>si</strong>ć in V. Batagelj: Verjetnostni račun in statistika 618<br />

✬<br />

Preizkuˇsanje regre<strong>si</strong>jskih koeficientov<br />

Po metodi momentov dobimo cenilki za α in β:<br />

B = R Cy<br />

Cx<br />

= Cxy<br />

C 2 x<br />

in A = Y − BX,<br />

kjer so C 2 x = n<br />

i=1 (Xi − X) 2 , C 2 y = n<br />

i=1 (Yi − Y ) 2 in<br />

Cxy = n<br />

i=1 (Xi − X)(Yi − Y ).<br />

Kako sta cenilki B in A porazdeljeni?<br />

B = Cxy<br />

C 2 x<br />

=<br />

n<br />

i=1<br />

Xi − X<br />

C 2 x<br />

(Yi − Y ) =<br />

Ker proučujemo pogojno porazdelitev Y glede na X (torej so vrednost X<br />

poznane), obravnavamo spremenljivke X1, . . . , Xn kot konstante.<br />

Ker je B linearna funkcija spremenljivk Y1, . . . , Yn, ki so normalno<br />

porazdeljene Yi : N(α + βXi, σ), je tudi B normalno porazdeljena.<br />

✫<br />

n<br />

i=1<br />

Xi − X<br />

C 2 x<br />

Univerza v Ljubljani ▲<br />

❙ ▲<br />

▲<br />

Yi.<br />

● ❙ ▲<br />

▲<br />

☛ ✖<br />

▲<br />

✩<br />

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