B5.073 - Prework Satterwite

Question 1

sensitivity definition

Answer 1

Probability of test being positive given that disease is present. Sensitivity is the ability of a test to correctly identify people with a disease.

Question 2

sensitivity equation

Answer 2

true positives/(true positives + false negatives), or the probability of a test being positive given that disease is present.

Question 3

specificity definition

Answer 3

Ability of a test to correctly identify people without a disease.

Question 4

specificity equation

Answer 4

true negatives/(true negatives + false positives), or the probability of a test being negative given that disease is not present.

Question 5

PPV

Answer 5

If a test result is positive, how often does the patient have the disease?
Positive predictive value (PPV) is the probability of a person having a disease given that the test is positive. The equation is true positives/(true positives + false positives).

Question 6

NPV

Answer 6

Negative predictive value (NPV) is the probability of a person not having a disease given that the test result is negative. The equation is true negatives/(true negatives + false negatives).

Question 7

In a clinical scenario, how can a test result from a test with high specificity can be most useful?

Answer 7

A positive result can be used to rule in disease.
Tests with high specificity do a good job identifying people without disease (lots of people without disease have a negative test; there are many true negatives). The flip side is that someone who does have the disease might also be incorrectly classified as having the disease by having a positive test result (false negatives).

Question 8

tests with high sensitivity are good for

Answer 8

Tests with high sensitivity do a good job identifying people with disease (true positives), but someone who doesn’t have the disease might also incorrectly have a positive test result (false positives). Most negative results produced from a test with high sensitivity will likely be true negative results. Thus, a negative result from a highly sensitive test can be used to rule out disease.

Question 9

When a man is screened for colorectal cancer and has a positive test result but ends up not having colorectal cancer, what is this called?

Answer 9

false positive

Question 10

What is “overdiagnosis” in the context of breast cancer screening?

Answer 10

Overdiagnosis refers to cancers that are not clinically apparent and will not result in future death. Overdiagnosis pertains to slow-growing cancers. Cancers that are overdiagnosed can be cured but do not need to be cured. The proportion of cancers that are overdiagnosed is estimated at a population level. As screening increases and disease diagnosis increases, mortality due to the disease of interest is considered. If mortality rates remain relatively stable despite these increases, this is suggestive of overdiagnosis (screening is detecting more cases, but not preventing death).

Question 11

How does using risk-based screening criteria impact the predictive value of a test?

Answer 11

Using risk-based criteria to define a group of people eligible for screening creates a population at a higher risk for disease. Thus, the disease will be more common in this population (the prevalence will be higher). When the disease is more common, a person who has a positive test result is more likely to actually have the disease. The probability of disease given a positive test result (PPV) is higher.