module 2 Flashcards
what do we mean when we ask if the diagnostic tests are accurate
does the diagnostic test provide sufficient information to reliably distinguish individuals with or without the condition of interest
how much does the probablity change pre and post test
are diagnostic clinical test ever 100% accurate
no
- there is alway a chance of false negatives and positives
what does sensitivity address
how good in the test ID people with the disease
snOUT - rule out
what does specificity addres
how good is the test at ID without the disease
spIN
what does the positive predictor rule address
if a person test positive - what is the probability that they have the condition
ID those who have the disease amongst those who tested positive
what does the negative predictor rule address
if a person test neg, what is the prob that they do not have the condition
ID those who do not have the disease among those who have a neg test result
positive LR addresses
how much more likely is a positive test found in someone with the disease than in someone without it
negative LR addresses
how much more likely is a neg found in someone without the disease compare to someone who has it
is sensitivity a true positive or true negative rate
true positive
test with high sensitivity have few false negatives
therefore neg result rule out the condition
is specificity a true positive or true negative rate
true negative
have few false positives so if you have a positive it rules in the conditions
false positives impact spin or snout
spin
false negative impact spin or snout
snout
what is the difference between sn/sp and PPV/NPV - sn/sp
calculated from those who have the disease and those who do not
stable regardless of the disease prevelence in different populations
what is the difference between sn/sp and PPV/NPV - PPV/NPV
calculated from those who are positive and those who are negative
influence by disease prevelance
pre test and post test sn/sp
sn/sp do not provide us information on shift from pre and post test
LR and pre and post test
these can tell about the shift pre and post test
qualifies the shift from pre and post test
what does LR examine
how likely the disease is given a positive or negative test result
postive LR - what does it tell us
given a positive test, are the odds the odds of having the condition larger
expresses the change in odds favoring the condition during a positive test
negative LR - what does it tell us
express the changes in odds favoring the codition given a neg result
given a neg result, are the odds of the condition smaller
what is pre test probality
what we know before applying the diagnostic test
clinician best guess
post test probability
what we know after applying the DTI
can be quatified by using LR
large positive LR indicates what
the condition is more likely
small negative LR indicates what
the condition is less likely
high specificity and +LR
larger + LR
due to the low false positive rate
high sensitivity and -LR
small -LR rate
due to low false negative
how can we tell the precision of the diagnostic accuracy esitmates
CI
- do not want to cross 0
if you have a larger CI is your information precise
no
over all what is the reason why we use LR
show the change in probability pre and post test
how do you know if a diagnostic test is reliable, accurate, and precise
is the test reproducible - good intra and inter rater reliablity
how accurate is the test (sn, sp, LR)
Intrarater reliability
how consistent an individual is at measuring a constant phenomenon
interrater reliability
how consistent different individuals are at measuring the same phenomenon
what % of sp or sn is good
80
sp + sn test to avoid
do not equal at least 100
what is youdans index
showing the diagnostic perfromance of a test
sn + sp - 1 >.5 (ideally 1)
what is a reciever operant curve
used when there is an overlap between those with or without a presentation
graphic method to calculate sn and sp when a range of test scores are bing considered
what is an ROC used for
determine the optimal cut value between healthy and disease states
determine the MCID
what is plotted on ROC’s
true positive rate vs false positive rate
where is the optimal threshold value found in ROC
in the point closest to the upper left corner
what does the area under thee curve depend on
the true positive rate
a large area under the curve tells us what
better diagnostic accuracy
what happens if the AUC is a flat line
this is a worthless test
AUC = .5
