Diagnostic Accuracy Tests

Question 1

How does a test help?

Answer 1

• a test is useful if our ability to predict whether a person has a condition or not… this is what guides treatment
• the probability of a condition before the test should be altered by the test result

Question 2

Why measure test accuracy?

Answer 2

• most tests make arrows even if correctly performed

Question 3

What is test accuracy?

Answer 3

• a comparison between..
  The disease state estimates by a test of interest (the index test)
  and
  The best estimate of the true disease state (the reference standard)
  –> It is the explicit recognition that most tests make errors even if correctly performed

Question 4

Describe the basic design to assess test accuracy

Answer 4

• series of patients
• index test
• reference standard
• blinded cross-clarification

Question 5

What are the important components of a test accuracy question?

Answer 5

• Participants: presentation, prior tests
• Index test
• Target Disorder
• Reference standar

Question 6

What is a reference standard?

Answer 6

• allows us to check if the index test results, are in fact correct. It is how the outcome (test accuracy) is measured
• must be more accurate than the index test

Question 7

What is a composite reference standard?

Answer 7

• a reference standard made up of more than one test

Question 8

What are the 4 components of critical appraisal of a test accuracy study?

Answer 8

• internal validity (potential for bias)
• what are the results
• can i apply the results to my patients (appplicability)
• what would be the impact of using the index tests in my patients/population

Question 9

What are the 3 types of bias that may arise in Diagnostic Test Accuracy studies?

Answer 9

• spectrum bias
• verification bias
• review bias

Question 10

What is spectrum bias?

Answer 10

• Are the characteristics of the tested population clearly described; did the stuffy aboard innapropritae exclusions?
• Ensure difficult to diagnose patients are not purposefully excluded - the will make the index test appear more accurate than it will be in practise

Question 11

What is verification bias?

Answer 11

• did all participants get both index test and reference standard?
• there is a tendency or patents with negative index tests to not get the reference standard

Question 12

What is review bias?

Answer 12

• was the index test interpreted without knowledge of the reference standard results and vice versa?
• if interpretation of the index test is not independent of there reference standard this has the potential to make the index test appear more accurate than it actually is

Question 13

Construct a 2x2 table and show how to derive sensitivity and specificity from it

Answer 13

see booklet

Question 14

How is sensitivity interpreted?

Answer 14

• How close is sensitivity to 100%?
• Higher the sensitivity the lower the false negative rate
• Sensitivity tells us about the usefulness of the test in ruling OUT a condition

Question 15

How is specificity interpreted?

Answer 15

• How close in specificity to 100%?
• Higher the specificity the lower the false positive rate
• Specificity tells us about the usefulness of the test in ruling IN a condition

Question 16

What questions need to be asked when assessing applicability?

Answer 16

• was there a clear study question?
• can the study results be applied to your patients
• can the index test be applied in your healthcare setting/in your patients

Question 17

The accuracy of many index tests can be influenced by:

Answer 17

Variation in technology 
- old vs new test technology 
- different test manufacturers
- fixed vs mobile 
- lab vs bedside tests 
Who performs them and interprets them 
- experience 
- skill