Trong thuc te' ctia cue iltig d;ing nhfin ‹1i;ng u, don gum ta chi cén sit d;ing mot lufit quyet d)mh nhu c:ie ’rig thuc (1-2a) va (1-7c) klii do sé tao ra nhiéu biéu quyet dinh, va rat de xuat hieu ohiéu cr trong dii lieu, tinh huéing den do chinh xiic ciia c:ie tinh toiin phiin 1éip. Nhiéu quye't dinh co the thay doi 1dp dupe gén chi vcri mot dieu chinh nho. Nghia la thuc té, phiin 1éin c:ie u mang d)ac diem
ciia ca 2 16p. Doi voi cue u nhu vay, thich hpp cho vec d)at chting trong mot 1ép d)ac
' ring d9ng, nhu, trong tinh c y Ie, noi ranh gicri giiia binh thuéing va khiic thuéing la cén phai phén tich them. Mot c:ich giai quye't la g mot sw dinh tinh(qualifications ) trong viec tinh torn xiic suat hau nghiem P(m,|x) cho 1dp in›. Chung han chiing ta gan dinh tinh "definite" néu xiic suat 16n hon 0.9, probable neu xiic sufit giira 0.9 va 0.8, va
"possible" néu xiic suat be hon 0.8. Theo ciich my thi vcri nut chai co case 55 (xem hinh 11) sé dupe phan 16p la mol ”possible” cork céa lép “super”, va case 54 la mot
”probable“ cork ctia top ”average”
Thay vi gan tinh vao 1ép nh)an dupe, mot phuong phiip khiic dupe su d;;ng trong mot so truéing hpp nhat d)mh do la guy d(mh cho su ton tai cua mot 1dp da)c biet goi la 1érp tit choi hay 1:i mien quyet du) ih (reject region).
Ky hieu:
m*: 1ép dupe phfin;
in,: 16p voi xiic suiit hau nghi(em cue dai, ch%g han P(m,|x) = max P(w |x) Lua)t Bayes co the viét nhu sau m*= in,
Bay gio ta guy d]nh xiic suat hau nghiem ctia mot nut chai phiii cao hon nhie’u so voi mot ngufing tu“ choi (reject threshold) nhat dinh , néu khong no sé dupe phén vao reject class w,. Cong thiic Bayes dupe viét lai nhu sau:
(1-14)
Khi tinh torn ti so hpp 1y (likelihood rzitio) véri so x:ie suat tién nghi(em
lprevalence rzitio), thi ta phai nhfin ti so my véri (1-9)/¶. Mot 16p c khong bao gicr co
mot rejection néu < (G-1)/c, do do k C [(c-1)/c, 1]. Thufit toiin Bayes va ting d;ing
Chting ta ’nnh boa khiii ni(em reject class su ding du lieu cork stoppers. GU su réng mot reject threshold = 0.7 la ngitfing dupe quy dinh. Tinh bie“n quyet dinh cho reject class la dii de xiic dinh ham phén 1crp voi cue xiic suat tién nghi(em P(in;) = 1-¶ = 0.3, P(in ) = 1-¶ = 0.7. Cum duéing théng quyet dinh la cue duéng
nghiéng va giao vcri tru.c tung tai PRT10=15.5 va PRT10=20.1. Chti y rang hai duéing my co xu hu6ng doi xfing nhau qua duéing th%g quyet d(uih da dupe xiic dinh. Hinh 12 la biéu do phan tiin véii cue dufing quyet dinh moi. viing o giira hat
duéing thang la reject
Hinh 12 - f uscn remnant siiul y.v is f‹ir t u ‹i cf usse.s ‹if c‹›rk strippers u ith rejnt regic›n hei wee n the s‹›I ic1 I mcs e‹irresponcl i iig tn reject thre.shc›ld J,=G. 7
Chfing ta hay xem cue ma tra)n phfin 1dp hieu thi trong Hinh 13. Nho lai mot chiit ta se thay rang co 4 u ctia 1éip 1 va 5 u ciia 1dp 2 bi phén 16p sai, la mm trong reject region chie'm 9% so u. So tuong phan 1dp sai bay gici cho 1ép 1 la lmau va cho 1dp 2 la 5 mau, tong so loi la 6%.
Rovs . Obscrv . c1assz I
€ots I I
Hinh 13: Classification matrices” of lw0 classes of cork st0pj›eo willj
prrral‹acrs zdjust«l for ihc rr]cct region boundaries. Thua)t toiin Bayes va ting
d;ing