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Diagnosis

Diagnosis. Computation of Post Test Probability. Sensitivity and Specificity. Using Sen. and Spec. to Revise Probability. We often use maternal serum α-fetoprotein (MSAFP) test to screen the fetal abnormalities. Pretest Probability = P(D + ) = 0.20 Sensitivity = P(T + |D + )=0.34

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Diagnosis

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  1. Diagnosis Computation of Post Test Probability

  2. Sensitivity and Specificity

  3. Using Sen. and Spec. to Revise Probability We often use maternal serum α-fetoprotein (MSAFP) test to screen the fetal abnormalities. Pretest Probability = P(D+) = 0.20 Sensitivity = P(T+|D+)=0.34 Specificity = P(T-|D-)=0.86 →PV+=? →PV-=?

  4. Methods to Revise Probability • 2 by 2 Table Methods • Decision Tree Methods • Bayesian Methods • Likelihood Ratio Methods

  5. The 2 by 2 Method (1)

  6. The 2 by 2 Method (2)

  7. The 2 by 2 Method (3) PV+=P(|D+| T+)=68/180=0.378 PV-= P(D-|T-)=688/820=0.839

  8. T＋= 0.34 6.8 % D＋= 0.2 T－= 0.66 13.2 % 11.2 % T＋= 0.14 D－= 0.8 68.8 % T－= 0.86 Decision Tree Method (1)

  9. D＋ 6.8 % T＋= 18 % D－ 11.2 % 13.2 % D＋ T－= 82 % 68.8 % D－ Decision Tree Method (2)

  10. Bayesian Methods

  11. Likelihood Ratio Method (1)

  12. Likelihood Ratio Method (2)

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