Class 26-28: Screenings In medicine Flashcards
What’re 2 questions pt.’s should always ask their md’s?
How accurate is the screening test you’re recommending?
Based on test results, how confident will you be in your prediction of whether I do or don’t have the Dz?
Sensitivity and specificity looks at which question?
How accurate is the screening test?
4 screening outcomes:
True positive
True negative
False positive
False negative
When someone w/ Dz is tested positive
Box A
True positive
When someone w/o Dz is tested negative
Box D
True negative
Rows on 2x2 table for medical screenings:
Positive
Negative
—instead of yes/no
True positive is in which box for 2x2?
Box A
True negative is in which box for 2x2?
Box D
When someone w/ Dz is tested negative
Box C
False negative
When someone w/o Dz tests positive
False positive
False positive falls in which box of 2x2?
Box B
False Negative is in which box for 2x2?
Box C
How well a test can detect presence of Dz:
Sensitivity
Positivity of test in the diseased
Rule out Dz
Sensitivity
Looks at the % of true positives
Sensitivity
Proportion of time that a test is POSITIVE in a patient that DOES have the Dz
Sensitivity
If a test is either highly-sensitive that test is said to have a low:
A low false-negative rate
How to calc sensitivity?
TP /
TP + FN
OR
TP /
All Dz
How well a test can detect absence of disease when Dz is absent :
Specificity
Negativity of test in the healthy
Rule out Dz
Specificity
Proportion of time that a test is NEGATIVE in a pt. That does NOT have Dz
Specificity
A highly specific test is said o have a low…
False positive rate
Looks at % of time ppl w/o Dx get a negative test:
Specificity
How to calc specificity:
TN /
TN + FP
OR
TN /
All not Dz
Sensitivity is asso. W/ which box on 2x2?
Box A
Specificity is asso. W/ which box on 2x2?
Box D
Positive predictive value and negative predictive value answer which MD question?
How confident are you in test results?
How accurately a positive test predicts the PRESENCE of Dz
PPV
% of TP’s in pt.’s w/ a positive test (correct prediction)
PPV
Also called PVP-Predictive value-positive
How to calc PPV?
TP /
TP + FP
OR
TP /
All positive tests
PPV is asso. W/ which box on 2x2?
Box A
NPV is asso. W/ which box on 2x2?
Box D
How accurately a negative test predicts the ABSENCE of Dz
Negative predictive value
-NPV
% of TN’s in pt.’s w/ a negative test (correct prediction)
NPV
Also, called PVN predictive value-negative
How to calc NPV?
TN /
TN + FN
OR
TN /
All negative tests
Proportion of time that a pt. Is correctly identified as either having a Dz or not having a Dz w/ a positive or negative test
Diagnostic accuracy (DA) or diagnostic precision (DP)
How to calc DA?
TP (box A) + TN (box D) / all pt’s
Ratio of the probability of a given test result for a person w/ the Dz / probability of the same test result for a person w/o Dz
Can be calc for both + and - results
Likelihood ratio (LR)
Probability of a + test w/o Dz
LR+
Probability of a - test w/ Dz / probability of a - test w/o Dz
LR-
What should LR+ be if beneficial?
> 10
What should LR- be if beneficial ?
<0.1
Ability to accurately discern btw those that DO and those that DONT have Dz
Validity
Extent to which results accurately reflect what was being assessed
Internal validity
Extent to which results are applicable to other populations
Generalizability
External validity
Ability of a test to give the same results on repeated uses
Reproducibility
Reliability
A valid test is always ______, yet a ______ test is not always ________
Reliable, reliable, valid
Many diagnoses typically have 2 dichotomous outcomes (+,-)
Multiple cutoff values
For screening test w. Numerical values, we use what for more efficient way to show a relationship btw sensitivity and specificity for tests w/ numerical outcomes?
ROCs
Receiver operator curves
