screening and diagnosis Flashcards
screening is used for ___
asymptomatic patients
early detection is only helpful if ___
early intervention is available and helpful
diagnosis is used for___
symptomatic patients
diagnostic tests need higher levels of ___
precision and accuracy
validity of test
how well does test measure what it is intended to
reliability of test
repeated measurements yield same result
what is a measure of reliability?
precision
typical reference range
2 SD from the mean (derived from healthy patients)
what increases the likelihood of an abnormal test?
increased number of tests performed
define sensitivity
patients with disorder are positive
SNOUT
tests with high sensitivity, a negative test can rule out
sensitivity equation
true negative = sensitivity x all negatives
define specificity
patients without disorder are negative
SPIN
tests with high specificity, positive tests rule in
specificity equation
true positives = specificity x all positives
PPV
patients with disease test positive
NPV
patients without disease test negative
what is more reliable than predictive values?
likelihoods ratios
3 reasons why gold standard tests aren’t always used
pose hazards, too costly, take too much time
pre-test probability
probability that pt has disease before test is run
pre-test probability is equal to
population prevalence
if performing several tests, the ___ of the first becomes the ___ of the next
post-test probability; pre-test probability
+LR equation
sensitivity/1-specificity
-LR equation
1-sensitivity/specificity
interpretation of LR greater than 1
post-test probability will be greater than pre-test probability
interpretation of LR less than 1
post-test probability will be less than pretest probability
interpretation of LR = 1
no difference in pre/post test probability
to confirm disease, use test with high ___
specificity
2 x 2 table equation for sensitivity
A/(A+C)
2 x 2 table equation for specificity
D/(D+B)
2 x 2 table equation for PPV
A/(A+B)
2 x 2 table equation for NPV
D/(D+C)
2 x 2 table equation for +LR
sensitivity/1-specificity
2 x 2 table equation for -LR
1-sensitivity/specificity
