Diagnostic Test Accuracy Studies Flashcards
Reasons for carrying out a diagnostic test
Detection / exclusion - we need to rule out a disease/
Make sure you’re not missing anything out
Legal / financial reasons
Protocols
The patient should be better off for having a diagnostic test (the probability of the condition before the test should be altered by the test result)
Name 2 reasons why it is important to evaluate medical tests?
avoiding evaluation bypass
medical tests are not regulated in the same way as treatments
What 3 things might cause evaluation bias?
enthusiasms
convictions
commercial pressure
What are the consequences of false positives?
stress + anxiety
unnecessary further tests and treatement
What are the consequences of false negatives?
wrongly reassures patients
results in disease being missed
harm to others (infectious diseases)
How might a new test be beneficial even if it has a slightly worse accuracy?
cheaper easier less invasive safer quicker
What about a DTA makes is a useful indication of the potential value of a test?
they are readily available in contrast to test treat RCTs
they don’t require prohibitively large sample sizes
answers can be obtained quickly
What is sensitivity in DTA?
what proportion of those with the disease does the test detect?
What is specificity in DTA?
what proportion of those without the disease get negative test results?
What are the components of PITR?
Participants (presentation, prior tests before index test)
Index test (conduct, technology)
Target disorder
Reference standard (the most accurate method available of detecting the target disorder)
What do we mean by blinded cross-classification?
comparing the results of the index test and reference standard for detection of target disorder
Name 3 key sources of bias in a DTA
Spectrum bias
Review bias
Verification bias
When might spectrum bias arise?
What questions might combat this?
If ‘difficult to diagnose’ patients are purposefully excluded –this will make the index test appear more accurate than it will be in practice
Are characteristics of the tested population clearly described; did the study avoid inappropriate exclusions?
When might review bias arise?
What questions might combat this?
If interpretation of the index test is not independent (and blind) of the reference standard -this has the potential to make the index test appear more accurate than it actually is
Was the index test interpreted without knowledge of (blind to) the reference standard result and vice versa?
When might verification bias arise?
What questions might combat this?
There is a tendency for patients with negative index test results not to get the reference standard -this will result in over or under estimation of the accuracy of the index test
Did all the participants get both index test and reference standard?
