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Statistika (za biologe, 2.dio) - Pmf

Statistika (za biologe, 2.dio) - Pmf

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Normalna aproksimacija<br />

Kao prvu diskretnu razdiobu uveli smo binomnu razdiobu, tj. X ∼ B(n, p).<br />

Kao ˇsto znamo ova sl. varijabla ima očekivanje np i varijancu npq, pa nam<br />

sljedeća transformacija<br />

X − np<br />

√ npq<br />

daje sl. varijablu koja ima očekivanje 0 i varijancu 1. No to i dalje ostaje<br />

diskretna razdioba. Zbog toga je moˇzda iznenadjujuće da <strong>za</strong> sve 0 < p < 1<br />

� �<br />

X − np<br />

P √ ≤ x ≈ P (Z ≤ x),<br />

npq<br />

gdje je Z ∼ N(0, 1) <strong>za</strong> dovoljno velike n.

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