Diagnostic Accuracy Tests Flashcards

1
Q

How does a test help?

A
  • 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
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2
Q

Why measure test accuracy?

A
  • most tests make arrows even if correctly performed
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3
Q

What is test accuracy?

A
  • 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
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4
Q

Describe the basic design to assess test accuracy

A
  • series of patients
  • index test
  • reference standard
  • blinded cross-clarification
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5
Q

What are the important components of a test accuracy question?

A
  • Participants: presentation, prior tests
  • Index test
  • Target Disorder
  • Reference standar
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6
Q

What is a reference standard?

A
  • 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
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7
Q

What is a composite reference standard?

A
  • a reference standard made up of more than one test
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8
Q

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

A
  • 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
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9
Q

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

A
  • spectrum bias
  • verification bias
  • review bias
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10
Q

What is spectrum bias?

A
  • 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
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11
Q

What is verification bias?

A
  • 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
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12
Q

What is review bias?

A
  • 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
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13
Q

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

A

see booklet

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14
Q

How is sensitivity interpreted?

A
  • 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
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15
Q

How is specificity interpreted?

A
  • 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
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16
Q

What questions need to be asked when assessing applicability?

A
  • 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
17
Q

The accuracy of many index tests can be influenced by:

A
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