Week 13

Question 1

What are false positives and false negatives? (2)

Answer 1

False positive:
When a test is positive when the disease is actually not present

False negative:
When a test is negative when the disease is actually there

Question 2

What is sensitivity and how is it calculated? (4)

Answer 2

The proportion of people with the disease that have a positive test
Used to rule out a disease
No false negatives

Calculated by true positives / all positive cases

Question 3

What is specificity and how is it calculated (4)

Answer 3

The proportion of people without the disease that have a negative test
Used to rule in a disease
No false positives

Calculated by true negatives / all negative cases

Question 4

How are specificity and sensitivity balanced? (4)

Answer 4

If the test is made more sensitive, it will pick up more people with the disease, so it will be less specific

If the test is made less specific, the test is less sensitive and there will be more false negatives

Question 5

What is a positive predicative value and how is it calculated? (2)

Answer 5

The proportion of people with a positive test who have the disease

Calculated by true positive / all positive tests

Question 6

What is a negative predicative value and how is it calculated (2)

Answer 6

The proportion of people with a negative test who do not have the disease

Calculated by true negative / all negative tests

Question 7

What is disease prevalence and how is it calculated? (2)

Answer 7

The proportion of people in the population that have had the disease

Calculated by all positive cases / population tested