USMLE Step2 Secrets Biostatistics 1-5
Terms
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- Sensitivity is defined as ...
- The ability of a test to detect DISEASE
- How is sensitivity mathematically measured?
- The number of true positives divided by the number of people with the disease (meaning true positives and false negatives)
- Tests with high sensitivity are used for ...
-
Disease screening.
False positives (people who don't have the disease, but tested positive) occur, but the test does not miss many people with the disease (low false-negative rate, ie. people who tested negative, but actually have the disease) - Specificity is defined as ...
- the ability of a test to detect nondisease (detect health)
- Mathematically, how is specificity derived?
- The number of true negatives divided by the number of people without the disease (true negatives plus false positives)
- Tests with high specificity are used for
-
disease confirmation.
False negatives (people who tested negative, but actually have the disease), but the test does not call anyone sick who is actually healthy (low false-positive rate).
The ideal confirmatory test must have a high sensitivity AND high specificity, otherwise, people with the disease may be called healthy, meaning there is an unacceptably high false-negative rate. - If the cut-off serum glucose value of a diagnosis of DM is set very low, no cases of diabetes will be missed, but many people withou the diabetes will be mislabeled as diabetes ie...
-
higher sensitivity
lower specificity
lower PPV
higher NPV - If the cut-off is set very high, the diagnosis of diabetes will not be made in healthy people, but many cases of true diabetes will go undiagnosed ie..
-
lower sensitivity
higher specificity
higher PPV
lower NPV - When a test is positive for the disease, the PPV measures how likely it is that the patient ...
-
actually has the disease.
In other words, the probability of having a condition, given a positive test. - PPV is calculated by ...
- dividing the number of true positives by the number of people with a positive test.
- PPV depends on the ...
- prevalence of the disease.
- The higher the prevalence of a disease,
- the higher the PPV
- PPV depends also on the
- sensitivity and specificity of the test
- An overly sensitive test that gives more false positivies has
- a lower PPV