Interpreting Data Regarding Diagnostics Testing Flashcards
what is a gold standard?
a test that is considered to be consistently correct and to which other tests can be compared
–> best test available for any given condition
ex: autopsy results to determine disease presence
biopsy to determine malignancy
culture results to determine presence of a specific bacteria
what is reliablity
level of agreement between repeated measures of the same variable
synonymous with repeatability, test-retest reliability, and reproducibility
level of agreement between repeated measures of the same variability is:
reliability, repeatability, test-retest reliability, reproducibility
what is validity?
the extent to which a test actually rests what it claims to test
the extent to which a test actually rests what it claims to test is
validity
what are the quantitative measures of validity?
sensitivity, specificity, predictive values, and likelihood ratios
sensitivity, specificity, predictive values, and likelihood ratios are quantitative measures of:
validity
what is specificity of a test?
its ability to detect people who do not have a disease
-true positives)
=TN (true negative) /(TN+FP or total without the disease)
what is sensitivity of a test?
its ability to detect people who do have a disease
-true negatives
=TP (True positives) / (TP+FN or total with the disease)
TN/ TN+FP
specificity - detecting true positives
TP/TP+FN
sensitivity - detecting true negatives
why are sensitivity and specificity useful
-describes the quality of the test
what is the positive predictive value
likelihood that a person with a positive result actually has the disease
-answers what percentage of the positive results actually have the disease
=TP/TP+FP (true positives over all positives)
what is the negative predictive value
likelihood that a person with a negative result actually does not have the disease
=TN/TN+FN (true negatives over all negatives)
=TP/TP+FP (true positives over all positives)
positive predictive value
=TN/TN+FN (true negatives over all negatives)
negative predictive value
prevalence:
=TP+FN/total
true results over total results
describe the relationship between PPV/NPV and prevalence
PPV and NPV both depend on characteristics of test itself AND the prevalence of disease in a population
–> prevalence of disease dramatically affects PPV and NPV
why are PPV and NPV useful?
- more clinically useful than sensitivity and specificity because they depend both on the characteristics of the test and the prevalence of the disease in a population
- can answer the question how likely is it that a patient has or doesnt have the disease theyre being tested for
explain SNOUT
highly sensitive tests have very few false negatives (FN) therefore when a sensitive test is negative it can rule out a disease
explain SPIN
highly specific tests have very few false positives (FP) therefore when a specific test is positive it tends to rule in a disease
what is likelihood ratio (LR)?
value calculated by combining sensitivity and specificity of a test
the value calculated by combining sensitivity and specificity of a test is
the likelihood ratio
what does a positive LR mean?
=sensitivity / 1-specificity
test can rule in a disease
the higher the number, the more effective it is at ruling in a disease
what does a negative LR mean
=1-sensitivity/specificity
test can rule out a disease
the lower the number, the more effective it is at ruling out a disease
what is an ROC curve
plots the true positive rate against the false positive rate for different cutoffs of a diagnostic test
a highly specific test would generate:
a lot of false negatives
-would capture all the people without the disease, but this includes the tail of the group with the disease so this would give a lot of false negatives
a highly sensitive test would generate:
a lot of false positives
-would identify all the people with a disease but in doing so would include people without the disease
