Diagnostic Accuracy Tests Flashcards
How does a test help?
- 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
Why measure test accuracy?
- most tests make arrows even if correctly performed
What is test accuracy?
- 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
Describe the basic design to assess test accuracy
- series of patients
- index test
- reference standard
- blinded cross-clarification
What are the important components of a test accuracy question?
- Participants: presentation, prior tests
- Index test
- Target Disorder
- Reference standar
What is a reference standard?
- 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
What is a composite reference standard?
- a reference standard made up of more than one test
What are the 4 components of critical appraisal of a test accuracy study?
- 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
What are the 3 types of bias that may arise in Diagnostic Test Accuracy studies?
- spectrum bias
- verification bias
- review bias
What is spectrum bias?
- 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
What is verification bias?
- 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
What is review bias?
- 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
Construct a 2x2 table and show how to derive sensitivity and specificity from it
see booklet
How is sensitivity interpreted?
- 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
How is specificity interpreted?
- 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
What questions need to be asked when assessing applicability?
- 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
The accuracy of many index tests can be influenced by:
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