Week 2.2: Evidence about diagnosis

Question 1

What is an index test?

Answer 1

Diagnostic test of interest

Question 2

What is sensitivity?

Answer 2

Percentage of patients with the condition that had a positive test result using the index test

Question 3

How do you classify the group of participants who have the condition, but have a negative test result?

Answer 3

False negative

Question 4

What is the positive predictive value?

Answer 4

Probability that the patients with a positive test truly have the disease

Question 5

How do you calculate sensitivity?

Answer 5

True positive/true positive + false negative

Question 6

How do you calculate specificity?

Answer 6

True negative/true negative + false positive

Question 7

How do you calculate the positive predictive value?

Answer 7

True positive/true positive + false positive

Question 8

How do you calculate the negative predictive value?

Answer 8

True negatives/true negative + false negative

Question 9

How do you calculate positive predictive value?

Answer 9

True positive/true positive + false positive

Question 10

What do likelihood ratios predict?

Answer 10

Predict the presence of diagnosis

Question 11

How do you calculate the negative predictive value?

Answer 11

True negative/true negative + false negative

Question 12

What does SnNOut mean?

Answer 12

High sensitivity, negative, helps rule out

Question 13

What does SpPIn mean?

Answer 13

Specificity, positive, helps rule in

Question 14

What does a positive likelihood ratio represent?

Answer 14

How much more likely is a positive test to be found in a with person with the condition than in a person who does not have the condition

Question 15

What does a negative likelihood ratio represent?

Answer 15

How much more likely is a negative test to be found a person without the condition that in a person with it

Question 16

What are the significant positive likelihood ratio values?

Answer 16

= 1: useless
>2: helps rule in disease
>10: extremely good for ruling in disease

Question 17

What are the significant negative likelihood ratio values?

Answer 17

= 1: useless
<0.5: helps rule out disease
<0.1: extremely good for ruling out disease

Question 18

How is the likelihood ratio of a positive test calculated?

Answer 18

sensitivity/(1 - specificity)

Question 19

How is the likelihood ratio of a negative test?

Answer 19

(1 - sensitivity)/specificity

Question 20

What is a gold standard test?

Answer 20

The most accurate test available, regardless of how invasive, expensive or time consuming

Question 21

What does a cohort study involve? How does a cross sectional study compare?

Answer 21

People with a particular clinical presentation, who present at a particular hospital, undergo both the gold standard and index test, whereas in cross sectional studies, these people are recruited.

Question 22

What does a case-control study population involve?

Answer 22

• People who clearly have the disease
• People who clearly do not have the disease
  Both undergo gold standard and index test, to discriminate between extreme cases.

Question 23

What is specificity?

Answer 23

The percentage of people that do not have the condition that were correctly identified as a negative result with the index test