Diagnostic Accuracy Flashcards
Percent Accuracy
(True Positives + True Negatives) / Total # of Patients
Sensitivity (definition)
The capability of the diagnostic test to correctly classify individuals with the condition of interest (true positives)
Sensitivity (equation)
True positives / (true positives + false negatives)
Specificity (definition)
The capability of the diagnostic test to correctly classify individuals who do
not have the condition (true negatives)
Specificity (equation)
true negatives / (true negatives + false positives)
Accuracy of a test is heavily influenced by_______________
The prevalence of the condition
Prevalence
The number of cases of a
condition existing in a given
population at any one time
Positive Predictive Value (PPV) (definition)
An estimate of a diagnostic test to correctly determine the proportion of patients with the disease from all of the patients with positive test results
Positive Predictive value (equation)
True Positives / True positives and false positives
Negative Predictive Value (NPV) (definition)
An estimate of a diagnostic test to correctly determine the proportion of
patients without the disease from all of the patients with negative test results
Negative predictive value (NPV) (equation)
True Negatives / True negatives and false negatives
Pretest Probability
the likelihood a patient has a certain condition based on appearance and history before a diagnostic test.
Likelihood ratio
Combine sensitivity and specificity to evaluate the diagnostic accuracy of a test for an individual patient.
Positive Likelihood Ratio (LR+) (definition)
Indicates that a positive test result was obtained in a person with the condition as compared with a person without the condition
LR+ Equation
Sensitivity / (1 - Specificity)
(will give a number >1)
Negative Likelihood Ratio (LR-) (definition)
Indicates the likelihood that a negative test result was observed in a person
with the condition as compared with a person without the condition
LR- Equation
(1- Sensitivity) / Specificity
(will give a number <1)
Likelihood Ratio Guidelines
The closer LR+ and LR- are to 1 the less accurate the diagnostic test (closer to a coin-flip)
For clinicians,_________ are often more useful
predictive values
By themselves_______ and ________ are only useful when either is very high
sensitivity and specificity
Posttest probability
probability of a condition based on results of diagnostic test
