Lecture 105 - Sensitivity, Specificity, Predictive Values, and ROC Curves

Question 1

Sensitivity = Probability of a Positive test given a Positive state (for our purposes, the probability of testing positive for a disease give you have the disease).

So, Sensitivity =

Specificity = Probability of a True negaive given a Negative state.

Sensitivity =

Answer 1

Sensitivity = True Positives

Total Disease positive

Specificity = True Negatives

Total Disease Negative

Question 2

Preditive value of Positive Test (Positive predicitve value; PPV) = probability of Disease positive given a Positive Test

PPV =

Negative Predictive Value (NPV) =

Answer 2

PPV = True Positive Tests

Total Positive Tests

NPV = True Negative Tests

Total Negative Tests

Question 3

How is PPV related to Prevalance?

Answer 3

The higher the Prevalance, the greater the PPV.

Question 4

Likelihood Ratio positive (LR positive) =

LR negative =

Answer 4

LR positive = Sensitivity / (1 - Specificity)

LR negative = (1 - Sensitivity) / Specificity