Lecture 6 - Evaluating a diagnostic test

Question 1

_____ or ______ = the consistence and reproducibility of a test

Answer 1

precision, reliability

Question 2

____ or ____ = the trueness of test measures

Answer 2

accuracy, validity

Question 3

2 types of validity:
_____ = results of study are valid for sample of patients actually studied;

____ = results of study are generalized to others outside study group

Answer 3

internal;

external

Question 4

precision vs accuracy:
____ is the absence of random variation in a test;
____ is the absence of systemic error.

increased _____ lowers the standard deviation and increases statistical power

Answer 4

precision (reliability);
accuracy (validity)

precision

Question 5

____ is the proportion of all people with disease who test positive;

____ is the proportion of all people without the disease who test negative.

Answer 5

sensitivity;

specificity

Question 6

_____ = 1 - false negative rate

______ = 1 - false positive rate

Answer 6

sensitivity;

specificity

Question 7

values of ____ approaching 100% are useful for ruling in a disease. values of _____ approaching 100% are useful for ruling out a disease

Answer 7

specificity;

sensitivity

Question 8

highly _____ tests are used as screening tests in diseases with ____ prevalence. high _____ tests are used for confirmation

Answer 8

sensitive, low;

specific

Question 9

highly ____ tests have a low-false positive rate. highly ____ tests have a low false negative rate

Answer 9

specific, sensitive

Question 10

_____ is the proportion of negative test results that are true negatives. ____ is the proportion of positive test results that are true positives.

Answer 10

NPV, PPV

Question 11

PPV varies _____ with pretest probability/prevalence. NPV varies ____ with pretest probability/prevalence

Answer 11

directly (ie high prevalence = high PPV);

inversely (ie low prevalence = high NPV)

Question 12

lowering the cutoff value of a test ____ the false positives and ____ the false negatives. thus sensitivity _____, NPV ____, specificity _____, and PPV ____

Answer 12

increases, decreases;
increases, increases;
decreases, decreases

Question 13

raising the cut off value of a test _____ the false positives and ____ the false negatives. thus, sensitivity _____, NPV _____, specificity ____, and PPV ____

Answer 13

lowers, increases;
decreasess, decreases;
increases, increases

Question 14

equation for ____ = sensitivity / (1 - specificity);

equivalent to what other equation?

Answer 14

LR+ (likelihood ratio of a positive test);

True positive / False positive rate

Question 15

LR(-) = ______ / _____;

or _____ negative / _____ negative

Answer 15

(1 - sensitivity) / specificity;

false negative / true negative

Question 16

a LR+ > _____ or an LR(-) < _____ are indicators of a useful diagnostic test

Answer 16

10;

0.1

Question 17

likelihood ratio:
depend on prevalence or no?
an LR > 1 _____ chance of disease

Answer 17

do not depend on prevalence;

increases

Question 18

LR’s can be multiplied with ____ odds of a disease to estimate ___ odds

Answer 18

pretest;

post-test