Module 10 & 11

Question 1

Define “Sensitivity”

Answer 1

The measure of how well a test identifies the presence of a disease when it is present. TP out of all people with disease. SeNsitivity rules OUT (SNOUT). i.e., if a patient tests negative with a sensitive test, we can be more confident that they DON’T have the disease.

Question 2

Define “Specificity”

Answer 2

The measure of how well a test identifies the absence of a disease when it is absent. TN out of all people without disease. SPecificity rules IN. i.e., if a patient tests positive with a highly specific test, it is more likely they actually have the disease.

Question 3

Define “Positive Predictive Value”

Answer 3

TP out of all positives. Defines how well a positive result predicts disease.

Question 4

Define “Negative Predictive Value”

Answer 4

TP out of all negatives. Defines how well a negative result predicts absence of a disease

Question 5

How is the PPV related to prevalence?

Answer 5

The more prevalent a condition, the more greater the PPV is. i.e., if HIV positive in area where HIV endemic , you are more likely to have disease. If HIV positive where little HIV activity, less likely to have disease. Note that when PPV increases, NPV DECREASES.