Lecture 10 (Diagnosis)

Question 1

Sensitivity equation and table:

Answer 1

TP/(TP+FN)

SNOUT

Question 2

A sensitive test should be chosen when:

Answer 2

• there is an important penalty for missing the diagnosis.
• very few false negatives

Question 3

A specific test should be utilized when:

Answer 3

• false-positive can harm the patient physically, emotionally, or financially.
• used to “rule-in” diagnoses when data suggest.
• very few false positives

Question 4

Specificity equation and table:

Answer 4

TN/(TN+FP)

SPIN

Question 5

A sensitive tests yields:

Answer 5

• very few false negatives
• a lot of false positives
• SNOUT

Question 6

A specific test yields very few:

Answer 6

false positives

SPIN

Question 7

Positive predictive value:

Answer 7

• if test is positive, how likely it is a TP
• depends on sensitivity, specificity, and prevalence
• decreases as prevalence decreases

Question 8

Positive predictive value equation and table:

Answer 8

TP/(TP+FP)

Question 9

+PV depends on:

Answer 9

1. sensitivity
2. specificity
3. prevalence

Question 10

+PV decreases as:

Answer 10

prevalence decreases

Question 11

Negative predictive value:

Answer 11

• if test is negative, how likely it is TN

Question 12

Negative predictive value equation and table:

Answer 12

TN(TN+FN)

Question 13

False positive rate =

Answer 13

1 - specificity

Question 14

ROC Curves:

Answer 14

• plots sensitivity versus specificity
• closer you are to the upper left hand corner of the graph, the better the test is.

Question 15

Pre-test probability =

Answer 15

prevalence

Question 16

Posterior (post-test) probabilities are:

Answer 16

• the probability of disease after the test result is known
• likelihood ratios can be used to calculate probability of disease after a positive or negative test.

Question 17

Likelihood ratios:

Answer 17

• used to calculate probability of disease after a positive or negative test.
• ​tells you how many times more likely a test result is to be found in people with disease compared to people without disease

Question 18

Positive Likelihood Ratio equation:

Answer 18

LR+ = Sn / (1-Sp)

Question 19

Negative Likelihood Ratio equation:

Answer 19

LR- = (1-Sn) / Sp

Question 20

How to use a nomogram:

Answer 20

• Place straightedge at correct prevalence and likelihood values to get the post-test probability.

Question 21

Parallel testing:

Answer 21

• Test A or Test B or Test C must be positive
• if any one test is positive, the result is positive.
• high sensitivity

Question 22

Serial testing:

Answer 22

• Test A and Test B and Test C all must be positive
• if all tests positive, result is positive
• high specificity