lab6: logis+c regression and metrics · bernoulli trials would be 10, i.e., ... tp tp+fn fpr = fp...
TRANSCRIPT
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Lab6:Logis+cRegressionandMetrics
Department of Computer Science, National Tsing Hua University, Taiwan
2020.10.08
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Outline
• BriefReview:Logis+cRegression
- MaximumlikelihoodinLogis+cRegression
- Implementa+on
• CommonEvalua+onMetricsforBinaryClassifica+on
- ConfusionMatrix
- SoHClassifiers-ROCCurve
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Outline
• BriefReview:Logis+cRegression
- MaximumlikelihoodinLogis+cRegression
- Implementa+on
• CommonEvalua+onMetricsforBinaryClassifica+on
- ConfusionMatrix
- SoHClassifiers-ROCCurve
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MaximumLikelihood• Flippingcoin:wehavealreadyknowgroundtruthdistribu+on.
Forexample, and .P(x = head) = 1/2 P(x = tail) = 1/2
0
0.5
1
head tail
H, T, H, H, T, T …
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MaximumLikelihood• Flippingcoin:wehavealreadyknowgroundtruthdistribu+on.
Forexample, and .
• However,inmanytasks,thegroundtruthdistribu+onsareneverknown,e.g.,probabilitydistribu+onofgeMngCOVID-19.
P(x = head) = 1/2 P(x = tail) = 1/2
0
0.5
1
head tail
Is Patient?
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MaximumLikelihood• Theprocesstoapproximatethedistribu+on:
- First,weassumethepropor+onofpeoplediagnosedwithadiseasefollowsBinomialdistribu+on,e.g., .X ∼ Bin(A, ρ)
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MaximumLikelihood• Theprocesstoapproximatethedistribu+on:
- First,weassumethepropor+onofpeoplediagnosedwithadiseasefollowsBinomialdistribu+on,e.g., .Where isnumberofpersondiagnosed, isillnessrate.
X ∼ Bin(A, ρ)A ρ
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MaximumLikelihood• Theprocesstoapproximatethedistribu+on:
- First,weassumethepropor+onofpeoplediagnosedwithadiseasefollowsBinomialdistribu+on,e.g., .Where isnumberofpersondiagnosed, isillnessrate.
- Ifthereare4pa+entsoutof10people,thenumberofBernoullitrialswouldbe10,i.e.,
X ∼ Bin(A, ρ)A ρ
X ∼ Bin(10, ρ)
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MaximumLikelihood• Theprocesstoapproximatethedistribu+on:
- First,weassumethepropor+onofpeoplediagnosedwithadiseasefollowsBinomialdistribu+on,e.g., .Where isnumberofpersondiagnosed, isillnessrate.
- Ifthereare4pa+entsoutof10people,thenumberofBernoullitrialswouldbe10,i.e.,
X ∼ Bin(A, ρ)A ρ
X ∼ Bin(10, ρ)
P(X = 4 |ρ) = C104 ρ4(1 − ρ)(10−4)
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MaximumLikelihood
P(X = 4 |ρ) = C104 ρ4(1 − ρ)(10−4)
ρ
P(X
=4|
ρ)
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Outline
• BriefReview:Logis+cRegression
- MaximumlikelihoodinLogis+cRegression
- Implementa+on
• CommonEvalua+onMetricsforBinaryClassifica+on
- ConfusionMatrix
- SoHClassifiers-ROCCurve
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Logis+cRegression• Inlogis+cregression,wesolvemaximumlog-likelihoodinstead.
• Updatewithgradientdecent:
where
arg maxw
log P(𝕏 |w)
w(t+1) = w(t) − η∇wlog P(𝕏 | w(t))
∇wlog P(𝕏 | w(t)) =N
∑t=1
[y′�(i) − σ(w(t)⊤x(i))]x(i) y′� = y + 12
,
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Logis+cRegression
P(y | x; w) = σ(w⊤x)y′�[1 − σ(w⊤x)](1−y′ �)
SoHpredic+on
arg maxy
{σ(w⊤x),1 − σ(w⊤x)} = sign(w⊤x)
Labelpredic+on
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Outline
• BriefReview:Logis+cRegression
- MaximumlikelihoodinLogis+cRegression
- Implementa+on
• CommonEvalua+onMetricsforBinaryClassifica+on
- ConfusionMatrix
- SoHClassifiers-ROCCurve
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ConfusionMatrix• Asidefromaccuracy,itisimportant
toknowhowthemodelmakewrongpredic+ons.
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ConfusionMatrix• Asidefromaccuracy,itisimportant
toknowhowthemodelmakewrongpredic+ons.
• Inbinaryclassifica+on,confusionmatrixisacommontooltoanalyzethepredic+ons.
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ConfusionMatrix• Asidefromaccuracy,itisimportant
toknowhowthemodelmakewrongpredic+ons.
• Inbinaryclassifica+on,confusionmatrixisacommontooltoanalyzethepredic+ons.
Ground truth
Positive predictions of your model
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ConfusionMatrix• Asidefromaccuracy,itisimportant
toknowhowthemodelmakewrongpredic+ons.
• Inbinaryclassifica+on,confusionmatrixisacommontooltoanalyzethepredic+ons.
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ConfusionMatrix• Asidefromaccuracy,itisimportant
toknowhowthemodelmakewrongpredic+ons.
• Inbinaryclassifica+on,confusionmatrixisacommontooltoanalyzethepredic+ons.
• Manymetricsarederivedfromtheconfusionmatrix.
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ConfusionMatrix• Asidefromaccuracy,itisimportant
toknowhowthemodelmakewrongpredic+ons.
• Inbinaryclassifica+on,confusionmatrixisacommontooltoanalyzethepredic+ons.
• Manymetricsarederivedfromtheconfusionmatrix.
• e.g.
TPR =TP
TP + FNFPR =
FPFP + TN
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Outline
• BriefReview:Logis+cRegression
- MaximumlikelihoodinLogis+cRegression
- Implementa+on
• CommonEvalua+onMetricsforBinaryClassifica+on
- ConfusionMatrix
- SoHClassifiers-ROCCurve
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ROCCurve• ROCcurveanalyzetheperformancefor
everythresholdinsoHclassifiers.
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ROCCurve• ROCcurveanalyzetheperformancefor
everythresholdinsoHclassifiers.
• X-axis:FPR
• Y-axis:TPR
TPR =TP
TP + FN
FPR =FP
FP + TN
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ROCCurve
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ROCCurve• WhatisbestROCcurve?
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Homework• Homework:Lab6
- Lab6:Logis+cRegression,Metrics
• Bonus:Lab7,Lab8
- Lab7:SupportVectorMachine,k-NearestNeighbors
- Lab8:CrossValida+on,Ensemble
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Homework• Deadline:10/2023:59(Tue)
- Duetotheheavyworkloads,wehaveextendedthedeadline.
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Reference• hfps://bookdown.org/ccwang/medical_sta+s+cs6/sec+on-43.html
• hfps://bookdown.org/ccwang/medical_sta+s+cs6/bernoulli.html
• hfps://bookdown.org/ccwang/medical_sta+s+cs6/binomial.html
• hfps://bookdown.org/ccwang/medical_sta+s+cs6/likelihood-defini+on.html
• hfps://en.wikipedia.org/wiki/Sensi+vity_and_specificity
• hfps://github.com/dariyasydykova/open_projects/tree/master/ROC_anima+on
https://bookdown.org/ccwang/medical_statistics6/section-43.htmlhttps://bookdown.org/ccwang/medical_statistics6/bernoulli.htmlhttps://bookdown.org/ccwang/medical_statistics6/binomial.htmlhttps://bookdown.org/ccwang/medical_statistics6/likelihood-definition.htmlhttps://bookdown.org/ccwang/medical_statistics6/likelihood-definition.htmlhttps://en.wikipedia.org/wiki/Sensitivity_and_specificityhttps://github.com/dariyasydykova/open_projects/tree/master/ROC_animationhttps://github.com/dariyasydykova/open_projects/tree/master/ROC_animationhttps://bookdown.org/ccwang/medical_statistics6/section-43.htmlhttps://bookdown.org/ccwang/medical_statistics6/bernoulli.htmlhttps://bookdown.org/ccwang/medical_statistics6/binomial.htmlhttps://bookdown.org/ccwang/medical_statistics6/likelihood-definition.htmlhttps://bookdown.org/ccwang/medical_statistics6/likelihood-definition.htmlhttps://en.wikipedia.org/wiki/Sensitivity_and_specificityhttps://github.com/dariyasydykova/open_projects/tree/master/ROC_animationhttps://github.com/dariyasydykova/open_projects/tree/master/ROC_animation