Classes 26-28 Screenings in Medicine

Question 1

True Positive (TP)

Answer 1

Test correctly reports a positive result in a patient that actually does have the disease
(Box A)

Question 2

True Negative (TN)

Answer 2

Test correctly reports a negative result in a patient that actually does not have the disease
(Box D)

Question 3

False Positive (FP)

Answer 3

Test incorrectly reports a positive result in a patient that actually does not have the disease
(Box B)

Question 4

False Negative (FN)

Answer 4

Test incorrectly reports a negative result in a patient that actually does have the disease
(Box C)

Question 5

Sensitivity

Answer 5

How well a test can detect presence of disease when in fact disease is present – Positivity-of-test in the diseased
Proportion of time that a TEST is positive in a patient that does have the disease

Question 6

Sensitivity equation

Answer 6

Sensitivity = TP/(TP + FN) x 100%
Sensitivity = TP/(all Diseased) x 100%

Question 7

A highly sensitive test has:

Answer 7

A low false negative rate

Question 8

Specificity

Answer 8

How well a test can detect absence of disease when in fact the disease is absent – Negativity-of-test in the healthy
Proportion of time that a TEST is negative in a patient that does not have the disease

Question 9

Equation for Specificity

Answer 9

Specificity = TN/(TN + FP) x 100%
Specificity = TN/(All not diseased) x 100%

Question 10

A highly specific test has:

Answer 10

A low false positive rate

Question 11

Positive Predictive Value (PPV)

Answer 11

How accurately a positive test predicts the presence of disease
Percentage of TP’s in patients with a positive test (correct prediction)
Also referred to a predictive value-positive (PVP)

Question 12

Equation for PPV

Answer 12

PPV = TP/(TP + FP) x 100%
PPV = TP/(All Positive Tests) x 100%

Question 13

Negative Predictive Value (NPV)

Answer 13

How accurately a negative test predicts the absence of disease
Percentage of TN’s in patients with a negative test (correct prediction)
Also referred to as Predictive Value-Negative (PVN)

Question 14

Equation for NPV

Answer 14

NPV = TN/(TN + FN) x 100%
NPV = TN/(All Negative Tests) x 100%

Question 15

Diagnostic Accuracy (DA) or Diagnostic Precision (DP)

Answer 15

Proportion of time that a patient is correctly identified as either having a disease or not having a disease with a positive or negative test, respectively

Question 16

Calculation for DA (or DP)

Answer 16

= (TP/TN) / (TP + FP + FN + TN) x 100%

= (TP/TN) / (All patients) x 100%

Question 17

Likelihood Ratio (LR)

Answer 17

Probability of a given test result (positive or negative) for a person with the disease / probability of the same test result (+ or -) for a person without the disease

Question 18

Likelihood Ratio Positive (LR+)

Answer 18

Probability of a positive test in the presence of disease / probability of a positive test in the absence of disease

Question 19

Equation for Likelihood Ratio Positive (LR+)

Answer 19

[(A/(A+C)) / (B/(B+C))]

Sensitivity/(1-Specificity)

Question 20

Likelihood Ratio Negative (LR-)

Answer 20

Probability of a negative test in the presence of disease / Probability of a negative test in the absence of disease

Question 21

Equation for Likelihood Ratio Negative (LR-)

Answer 21

[(C/(A+C)) / (D/(B+D))]

(1-Sensitivity) / Specificity

Question 22

LR+ should be _____ to demonstrate the test is most beneficial.

Answer 22

> 10

Question 23

LR- should be _____ to demonstrate the test is most beneficial

Question 24

ROC (Receiver Operator Curves)

Answer 24

A more efficient way to show a relationship between sensitivity & specificity for tests with numerical (continuous) outcomes