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24 Cards in this Set
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Define Likelihood ratio (for a pos test):

How many times more/less likely a pos test result is found in a diseased vs nondiseased patient.


Formula for pos LR:

Sensitivity
 1  Spcfity 

Formula for neg LR:

1Sens
 Sp 

Define negative LR:

How many times more/less likely a neg test result is found in a nondiseased as compared to a diseased individual.


Formula for posttest odds:

Pretest Odds x Likelihood Ratio


what is the formula for pretest odds?

Prev
 1Prev 

So if a disease prevalence is 60% what are the odds of having the disease?

60:40


What does likelihood ratio do for interpreting Diagnostic testing?

Moves the estimated odds (probability) toward either end of the scale.


What is the tradeoff of increasing a test's sensitivity?

It will be accompanied by a decrease in specificity.


What feature of a ROC curve will show a most accurate test?

the closer the curve comes to the upper left corner of the roc space


What happens as the Roc curve comes closer to the 45degree diagonal of the roc space?

The less accurate the test is.


So a worthless ROC curve is:

a STRAIGHT DIAGONAL LINE


What represents the likelihood ratio on a ROC curve?

The slope of the tangent line at a given cutpoint.


What will give the highest LR?

The steepest slope


What does the area under the ROC curve represent?

Test accuracy


4 types of bias in diagnostic testing:

Spectrum bias
Leadtime bias Lengthtime bias Workup bias 

What is Spectrum bias?

When the study population has a higher disease prevalence than typical populations.


What is LeadTime Bias?

When detecting a disease earlier appears to increase survival duration but it's false.


What is length time bias?

When screening is more likely to catch lengthy cases because they are chronic and less rapidly fatal.


What is Workup bias?

When patients with pos or neg test results are preferentially referred to recieve verification of diagnosis by the gold standrd


Why is lead time bias not truly an increased survival duration?

Because the patient still dies at the same time, just knows they are diseased for a longer period of time.


If a screening test detects many more slow than rapidly growing tumors what type of bias is it?

Length time bias.


What is the 1st level of the Hierarchical model for diagnostic technology assessment?

Technical quality of the test  ie image quality, lab test reproducability.


What is the 2nd level of the Hierarchical model for diagnostic technology assessment?

Diagnostic accuracy of the test
sensitivity specificity 