Lecture notes
diagnostic test performance lecture
- Module
- Medicine
- Institution
- The University Of York (UOY)
includes: defining a disease, what is test and when is it used?, god standard, cut offs, predictive values, likelihood ratios
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1Week 6, Lecture
Diagnostic Test Performance
What defines a disease?
Criteria that must be met for an individual to be considered a case
o Clinical signs
o Biological indicators
o Survey responces
Set criteria is a test
What is a test?
A measurement of detection
A tool
Discrete or continuous outcomes
When do we use a test?
Disease surveillance
Diagnosis
Research
o Disease status
o Risk factors
Need to be aware of misclassification bias
Gold standard test applied to all individuals
Too expensive or invasive
Tests for widespread use
o Not always matched by those of the gold standard
May not completely align with the truth
Performance is how we quantify how good an alignment is
Positive test result does not always mean you have the disease
Negative test results do not always mean you do not have the disease
More complex
Tests are imperfect
Must decide thresholds for either doing or not something
Harms and benefits of treating and not treating
Must think carefully about the balance
The ideal
Consider a test based on a parameter that can be measured
Can often be substantial overlap and so some could be misclassified if you used cut
off parameters
Four groups
o Correct – true negatives and positives
o Misclassified – false negatives and positives
Can summarise against gold standard using a 2x2 table
Cut off values: a trade off
Minimised misclassification
Consequences of missing diseased individuals
Don’t want to do this for severe treatment options
Defining performance
A good test has the most people in true positive and true negative columns
Sensitivity
o How good a test is at finding a disease?
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