Diagnostic Studies Flashcards
Post-test probability
we estimate pre-test probability based on history and symptoms (YOU are deciding if it is positive or not)
after performing the diagnostic test, the likelihood ratio will determine our post-test probability
Negative likelihood ratio
the change in likelihood that a patient does not have a condition after a negative test
.2 to <.1 ratio
Positive likelihood ratio
the change in likelihood that a patient has the condition after a positive test
2 to above 10 ratio
Appraisal: results
Specificity
Sensitivity
NPV
PPV
What is the clinical bottom line?
is the test both accurate and clinically relevant to PT practice?
Will the resulting post-test probabilities affect my patient management?
Cutoff scores
end-feel, ROM, translation, etc
you need to keep the variable as the same, in order to become a viable parameter
SpPin
if your pt has a positive test result on a highly specific test, this can help you rule in a condition
high specificity means low false positives, likely that positive result is true
SnNout
if your patient has a negative test result on a highly sensitive test, this can help you rule out a condition
high sensitivity means low false negatives, like that negative result is true negative
Caution with Predictive Values
sensitivity and specificity are usually not impacted by prevalence of condition/disease
prevalence has a major impact on PPV and NPV, changing how the results are interpreted
NPV
proportion of negative tests that are true negatives
true negatives/total negative tests
PPV
proportion of positive tests that are true positives
true positives/total positive tests
Specificity
the accuracy of the test among people that do not have the condition/disease
True negatives/true - and false +
Sensitivity
the accuracy of the test among people that have condition disease
true positives/total between true + and false -
Appraisal for quality
Was the index test compared to gold standard test?
Did all participants receive both tests?
Were the diagnostic tests performed by two independent examiners?
Was the index test interpreted without other clinical info?
Were clinically useful stats included in the analysis and interpreted for clinical application?
QUADAS
quality assessment tool for diagnostic accuracy studies
