Epidemiology (IV) Multiple Test Screening

Question 1

What is a way to get around the decreased sensitivity and/or specificity of a particular test?

Answer 1

Provide two tests (either in sequence or in parallel); one should have a high sensitivity (screening test), and one should have a high specificity (confirmatory test)

Question 2

What are the two rules of sequential two-test screenings?

Answer 2

1. A positive test on the initial screen triggers a referral for the second test

(may apply if Test 1 is less ex­pensive, less invasive, or less uncomfortable, but Test 2 is more sensitive and specific)

2. Positive finding requires both tests to be positive

(if someone tests negative on EITHER test they are considered to not have the disease)

Question 3

What does sequential testing do to sensitivity and specificity?

Answer 3

It increases specificity and decreases sensitivity

(fewer false positives, but more cases missed)

Question 4

What does sequential screening do to false positive and false negative rates?

Answer 4

Fewer false positives (higher specificity); increased false negatives (higher sensitivity)

Question 5

What type of disease is amenable to sequential screening?

Answer 5

One where the damage done by a false positive would be very high.

Question 6

What is the rule of parallel (simultaneous) screening regarding positive outcomes?

Answer 6

Patient is defined as having the disease if they test positive on EITHER test

Question 7

What is the rule of parallel (simultaneous) screening regarding negative outcomes?

Answer 7

Patient is defined as disease-free if they test negative on BOTH tests

Question 8

What does parallel screening do to sensitivity and specificity?

Answer 8

Parallel testing increases sensitivity at the expense of specificity

(More cases are caught; but with more false positives)

Question 9

What type of disease is amenable to parallel screening?

Answer 9

One where missing the disease would have severe consequences

Question 10

What does parallel screening do to rates of false positives and false negatives?

Answer 10

Less false negatives (higher sensitivity); but with more false positives (lower specificity)

Question 11

Are sequential screenings better for sensitivity or specificity?

Are parallel screenings better for sensitivity or specificity?

Answer 11

Specificity (sequential)

Sensitivity (parallel)

Question 12

What does the positive predictive value measure?

Answer 12

If the test is positive, what’s the likelihood that the patient actually has the disease?

Question 13

Positive predictive value is similar to ________ that, if it is low, there will be an increase in ________.

Answer 13

specificity; false positives

Question 14

What is the formula for PPV?

Answer 14

TP / (TP + FP)

Question 15

What does the negative predictive value measure?

Answer 15

If the test is negative, what’s the likelihood that the patient is actually disease­-free?

Question 16

What is the formula for NPV?

Answer 16

TN / (TN + FN)

Question 17

What two factors most strongly influence PPV?

Answer 17

1. Specificity (sensitivity only marginally)
2. Disease prevalence

Question 18

If the PPV is very low, what does that indicate?

Answer 18

Either the test is not sufficiently specific, OR the population being tested has too low a disease prevalence for the test to be useful

Question 19

What are three types of variability across screening measurements?

Answer 19

Intra-subject, intra-observer, inter-observer

Question 20

What is intra-subject variability?

Answer 20

The tendency of a variable to fluctuate

Question 21

What is intra-observer variability?

Answer 21

The tendency of a single observer to get different results using the same test on the same person.

Question 22

What is inter-observer variability?

Answer 22

The tendency of two or more observers to get different results using the same test on an individual.

Question 23

What are a few methods of measuring variability among observers (e.g. screening staff; researchers; etc.)?

(OPA, PPA, KS)

Answer 23

Overall Percent Agreement

Paired Percent Agreement

Kappa Statistic

Question 24

What is an overall percent agreement?

Answer 24

The proportion of all tests in which the two observers provide the same rating

Question 25

What is a paired percent agreement?

Answer 25

A measure of the agreement between two tests/observers divided by the total number of pairs where at least one of the two tests/observers indicate a positive result

Since most people don’t have the disease and test negative, the percent agreement can be inflated because of the relatively large value in cell “d.”

So, this method simply ignores cell “d.”

Question 26

What is a kappa statistic?

Answer 26

Evaluates how much better the agreement between two tests/observers is than chance

Normally a value between 0 (no agreement) and 1 (comlpete agreement)