Gordis Epidemiology, 7th Edition TEST BANK By David D
Celentano; Moyses Szklo
What is a bimodal curve - ANSWER:a graph with two peaks that separates, for
example, those who have tuberculosis vs. those who do not from a screening test
unimodal curve - ANSWER:a graph with one peak, for example, blood pressure
readings
what is the validity of a test? What are its two components? - ANSWER:it's ability to
distinguish between who has a disease and who does not. Sensitivity and specificity
Sensitivity (true positives) - ANSWER:the proportion of diseased people who were
correctly identified as "positive" by the test. TOTAL WITH DISEASE IN DENOMINATOR
Specificity (true negatives) - ANSWER:the proportion of NON-diseased people who
were correctly identified as "negative" by the test. TOTAL WITHOUT DISEASE IN
DENOMINATOR
Sequential (two-stage) Screening - ANSWER:a less expensive, less invasive test is
performed first, and those who screen positive are recalled for further testing with a
more expensive, more invasive test
How to calculate net sensitivity and specificity in a two-stage screening program -
ANSWER:Take the numbers from a, b, and a+b from the first test and make that the
bottom total in the second test. Run the test. Then calculate sensitivity and
specificity as you would
Sequential testing results in a gain of ___________ and a loss of _______? -
ANSWER:Net specificity net sensitivity
Simultaneous Screening - ANSWER:Do both tests at once
How to be considered a true positive and true negative in simultaneous screening -
ANSWER:Positive: only need one positive result
Negative: BOTH tests must be negative
How to calculate net sensitivity in a simultaneous test - ANSWER:1. Find the number
of true positives in Test A
2. Run Test B's sensitivity on that number. This is the number of true positives found
by both tests A and B.
3. To find the number of true positives found ONLY in Test A, subtract it from the the
number found in step 2.
, 4. Do the opposite for test B.
5. Add test A only, Test B only, and both tests
Using a simultaneous test results in a net gain of ______ and net loss in _______ -
ANSWER:Gain in sensitivity and loss in specificity
What is in the denominator when calculating sensitivity? - ANSWER:People who have
the disease
What is in the denominator when calculating specificity? - ANSWER:People who do
NOT have the disease
What is the positive predictive value? - ANSWER:Focuses on the screening test, not
the disease. What is the chance that someone has the disease IF THEY TESTED
POSITIVE
What is negative predictive value? - ANSWER:What is the chance that someone does
not have the disease IF THEY SCREENED NEGATIVE
Positive predictive value equation - ANSWER:True positives/all who tested positive
Negative predictive value equation - ANSWER:true negatives/all who tested negative
What two factors is the positive predictive value affected by? - ANSWER:1.
prevalence of disease
2. specificity when the disease is rare
Relationship between positive predictive value and prevalence - ANSWER:direct - a
high prevalence raises the positive predictive value. Therefore, best for high-risk
populations
Relationship between positive predictive value and specificity of the test -
ANSWER:direct - an increase in specificity raises the the positive predictive value
What is the intrasubject variation in a screening test? - ANSWER:variability in
measuring human characteristics. Example: blood pressure readings taken from a
person when they have been sitting vs. moving- depends on time of day etc.
What is the intraobserver variation in a screening test? - ANSWER:variation between
two or more readings of the same test results made by the SAME observer
What is the interobserver variation in a screening test? - ANSWER:variation between
TWO OR MORE observers
What is the percent agreement? - ANSWER:The number of x-rays agreed upon
----------------------------------------- x 100
total number of x-rays read
Celentano; Moyses Szklo
What is a bimodal curve - ANSWER:a graph with two peaks that separates, for
example, those who have tuberculosis vs. those who do not from a screening test
unimodal curve - ANSWER:a graph with one peak, for example, blood pressure
readings
what is the validity of a test? What are its two components? - ANSWER:it's ability to
distinguish between who has a disease and who does not. Sensitivity and specificity
Sensitivity (true positives) - ANSWER:the proportion of diseased people who were
correctly identified as "positive" by the test. TOTAL WITH DISEASE IN DENOMINATOR
Specificity (true negatives) - ANSWER:the proportion of NON-diseased people who
were correctly identified as "negative" by the test. TOTAL WITHOUT DISEASE IN
DENOMINATOR
Sequential (two-stage) Screening - ANSWER:a less expensive, less invasive test is
performed first, and those who screen positive are recalled for further testing with a
more expensive, more invasive test
How to calculate net sensitivity and specificity in a two-stage screening program -
ANSWER:Take the numbers from a, b, and a+b from the first test and make that the
bottom total in the second test. Run the test. Then calculate sensitivity and
specificity as you would
Sequential testing results in a gain of ___________ and a loss of _______? -
ANSWER:Net specificity net sensitivity
Simultaneous Screening - ANSWER:Do both tests at once
How to be considered a true positive and true negative in simultaneous screening -
ANSWER:Positive: only need one positive result
Negative: BOTH tests must be negative
How to calculate net sensitivity in a simultaneous test - ANSWER:1. Find the number
of true positives in Test A
2. Run Test B's sensitivity on that number. This is the number of true positives found
by both tests A and B.
3. To find the number of true positives found ONLY in Test A, subtract it from the the
number found in step 2.
, 4. Do the opposite for test B.
5. Add test A only, Test B only, and both tests
Using a simultaneous test results in a net gain of ______ and net loss in _______ -
ANSWER:Gain in sensitivity and loss in specificity
What is in the denominator when calculating sensitivity? - ANSWER:People who have
the disease
What is in the denominator when calculating specificity? - ANSWER:People who do
NOT have the disease
What is the positive predictive value? - ANSWER:Focuses on the screening test, not
the disease. What is the chance that someone has the disease IF THEY TESTED
POSITIVE
What is negative predictive value? - ANSWER:What is the chance that someone does
not have the disease IF THEY SCREENED NEGATIVE
Positive predictive value equation - ANSWER:True positives/all who tested positive
Negative predictive value equation - ANSWER:true negatives/all who tested negative
What two factors is the positive predictive value affected by? - ANSWER:1.
prevalence of disease
2. specificity when the disease is rare
Relationship between positive predictive value and prevalence - ANSWER:direct - a
high prevalence raises the positive predictive value. Therefore, best for high-risk
populations
Relationship between positive predictive value and specificity of the test -
ANSWER:direct - an increase in specificity raises the the positive predictive value
What is the intrasubject variation in a screening test? - ANSWER:variability in
measuring human characteristics. Example: blood pressure readings taken from a
person when they have been sitting vs. moving- depends on time of day etc.
What is the intraobserver variation in a screening test? - ANSWER:variation between
two or more readings of the same test results made by the SAME observer
What is the interobserver variation in a screening test? - ANSWER:variation between
TWO OR MORE observers
What is the percent agreement? - ANSWER:The number of x-rays agreed upon
----------------------------------------- x 100
total number of x-rays read
