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
Appraisal for applicability
- Patient selection. Is there concern that pts do not match pts in question?
- Diagnostic Test. Is there concern that the test used is different vs test studied?
- Gold Standard. Condition studied does not match condition in question?
Components of Study Appraisal
- Appraisal for applicability
- Appraisal for quality
- Appraisal of results
- What is the clinical bottom line?
Comparative Studies
compares metrics between two or more diagnostic tests to a gold standard for a target population
study design should ensure a mix of patients that have and do not have the target condition generally cross-sectional, could be any study design
Diagnostic Case Control
compares metrics for a diagnostic test to a gold standard for a target population, it is already known who has the condition or disease and who does not.
study design by default ensures a mix of patients that have and do not have the target condition
Diagnostic Cohort Study
compares metrics for a diagnostic test to a gold standard over time for a target population
study design should ensure a mix of patients that have and do not have target condition
Types of Diagnostic Studies
Cross-sectional
Cohort
Case control
Comparative
Diagnostic Cross-Sectional Study
Compares metric for a diagnostic test to a gold standard at one point in time for a target population
study design should ensure a mix of patients that have and do not have target condition
What is a cohort study?
groups divided by shared characteristics that is not the condition can be retrospective or prospective
What is a case-control study?
groups divided by condition (cases vs control), usually retrospective
What is a quasi-experimental design?
lack either randomization or control group or both
there’s a lot of variation in quality, not put in the hierarchy b/c of this
5 As of EBP Process
Ask
Access
Appraise
Apply
Assess
Hierarchy of Evidence
CPGs
RCT
Cohort, Case Control
Cross Sectional
Case Series & Studies
Expert Opinions, Editorials
PICO statements
Patient
Intervention/dx/prognosis/etiology
Comparison
Outcome
What are the 5 steps of the EBP Process?
- Identify need for info
- Conduct lit search
- Critically appraise
- Integrate info
- Evaluate efficacy
3 Components of EBP model
Clinical Experience
Patient Preference
Research Evidence
