Chapter 6: Evidence about diagnosis

Question 1

What type of study is the best estimate of diagnostic accuracy of a test?

Answer 1

A consecutive cohort study, where it can be compared against the gold standard reference test.

Question 2

What is sensitivity?

Answer 2

The sensitivity of a test measures how well a test performs in detecting a disease in people who have the disease.

Question 3

What is specificity?

Answer 3

The specificity of a test measures how well a test performs in determining that disease is not present in people who do not have the disease.

Question 4

What does a post-test probability of a positive test tell you?

Answer 4

The post-test probability of a positive test (also known as positive predictive value) tells you the probability that a patient has disease if he or she has a positive test result. The closer that this number is to 100%, the better the test is at ruling in disease.

Question 5

What does a post-test probability of a negative test tell you?

Answer 5

The post-test probability of a negative test (which is the complement of the negative predictive value) tells you the probability that a client has the disease if he or she has a negative test result.

Question 6

What kind of studies measure the reliability of a test? What do they involve?

Answer 6

• Studies of inter-observer reliability: testing completed by different health professionals.
• Studies of observer reliability: testing completed by same health professional at different times.

Question 7

What are the main risks of bias in a diagnostic accuracy study?

Answer 7

• Only a selected portion of the patients can both the index test and the reference test.
• The results of the two tests are not interpreted independently to the other test or blinded to the results of the other test.