DTA Flashcards
What type of study do you use for evaluating diagnosis test accuracy?
Special cross-sectional study
What is meant by the evaluation bypass?
unevaluated procedure bypasses evaluation and becomes taken up by healthcare services
What can cause an evaluation bypass?
enthusiasm, convictions, commercial pressures
What makes a test useful?
If it changes our ability to predict whether a person has a condition or not. (guides treatment options)
What should a test result do?
Alter the probability of a condition being the suspected condition
Define test accuracy
The usefulness of a test result in diagnosing a patient. How good it the test at spotting who does/doesn’t have the disease?
Define diagnostic yield
How much information a diagnostic test can give - informs diagnosis
Define therapeutic yield
The amount it can impact the treatment decision
What do you need to consider beyond accuracy?
Harms - e.g. radiation, anxiety
Also is it reproducible? Would someone else doing the test get the same result?
More accurate may not improve outcomes - could be too late to intervene, may not change therapeutic input.
Tests for screening are…
Used for early identification of disease in asymptomatic patients (e.g. mammography)
Tests for monitoring are..
Used to monitor treatment response (e.g. blood glucose)
What do you compare for test accuracy?
Index Test and Reference Standard
What is the index test?
The disease state estimated by the test of interest
What is the reference standard?
The best estimate of true disease state (most accurate existing test)
What is blinded-cross classification and when is it used?
Comparison of the index test and reference standard. Compare the results blinded (without knowing)
What are the components of a test accuracy question?
Participants, index test, target disorder, reference standard
What are the components of participants in a test accuracy question?
- Presentation - presence, duration and severity of symptoms
- Prior test - have they been examined or self diagnosis, any bloods before
What components of the index test are important in a test accuracy question?
- Could be more than 1
- Could be a new test or unevaluated test
- Assumed to be less accurate than the reference standard
- Availability in primary versus secondary care
- Interpretation by the operator
What is the reference standard?
Most accurate and feasible method of detecting a target disorder, ‘gold standard’
Could be multiple tests
What are the parts of critical appraisal of a DTA study?
- Internal validity (bias)
- What are the results (numerical expression of test accuracy)
- Can I apply the results to my patient? (generalisability)
- What would be the impact of using the index tests in my population?
Define spectrum bias
Specific groups of patients are inappropriately excluded (e.g. difficult to diagnose patients). Makes the index test appear more accurate (selection bias)
Define review bias
Interpretation of the index test not independent to the reference standard. More common with subjective tests. Index test not blinded on interpretation.
Define verification bias
Not all participants get the index test and the reference standard. Often seen if the index test is negative
Define sensitivity
What percentage of people with the disease are picked up by the index test? Good at ruling people out.
