Deck 5: Assessing the Validity and Reliability of Diagnostic and Screening Tests

Question 1

A physical examination,digital rectal exam,was used to screen for prostate cancer in 290 men with biopsy-proven prostate cancer and in 516 age- and race-matched control men,all of whom showed no evidence of cancer at biopsy.The results of the physical examination were positive in 136 cases and in 165 control men.What is the sensitivity of the physical examination?

A) 32%
B) 47%
C) 56%
D) 57%
E) Cannot calculate it based on given information

Answer 1

B
Sensitivity equals the "number of people who identified as diseased by the test" divided by the "number of people who actually have the disease." The sensitivity is 0.47 (136 divided by 290).

Question 2

Two infectious disease epidemiologists want to investigate a new laboratory test that identifies TB infections.Dr.Merritt uses the standard test,which has a sensitivity of 80% and a specificity of 90%.Dr.Foundry uses the new laboratory test,which is 90% sensitive and 99% specific.Now,epidemiologists decide to run those two test as sequential tests (two-stage testing).What is the effect on net sensitivity of sequential tests?

A) 72%
B) 80%
C) 89%
D) 90%
E) 98%

Answer 2

A
In sequential screening tests,net sensitivity is a multiplicative value from each sensitivity value.Net sensitivity from sequential tests equals the sensitivity of test 1 multiplied by the sensitivity of test 2.The net sensitivity is 0.72 (0.8 multiplied by 0.9).

Question 3

A patient is weighed in the hospital by a nurse,and she is told she weighs 170 pounds.The next morning she weighs herself at home,and her weight is 168 pounds.Assuming that both scales were calibrated and the patient was measured under the same circumstances (no shoes,light clothing).What can explain the difference in weight?

A) Intrasubject variability
B) Intersubject variability
C) Intraobserver variability
D) Low specificity of the test
E) Low sensitivity of the test

Answer 3

A
Intrasubject variability refers to the changes that occur naturally over time in most variables measured for humans,such as weight,blood pressure,and blood glucose,among many others.

Question 4

Two physicians were asked to independently classify 250 ultrasounds as positive or negative.The comparison of their classification is shown in the following table.What is the simple percent agreement between the two physicians out of the total? Use the following table to answer the question. Number of Positive and Negative Cases by Physician 1 and Physician 2
$$\begin{array}{r}{ \text { Physician 1 } }\quad\quad\\\begin{array} { | l | l | l | } \hline{ \text { Physician } 2 } \\\hline & \text { Positive } & \text { Negative } \\\hline \text { Positive } & 45 & 15 \\\hline \text { Negative } & 25 & 165 \\\hline\end{array}\end{array}$$

A) 24%
B) 28%
C) 53%
D) 67%
E) 84%

Question 5

Two infectious disease epidemiologists want to investigate a new laboratory test that identifies tuberculosis (TB) infections.Dr.Merritt uses the standard test,which has a sensitivity of 80% and a specificity of 90%.Dr.Foundry uses the new laboratory test,which is 90% sensitive and 99% specific.In City A,it is known that 100 of 1,000 people have TB infections.What is the positive predictive value of the standard test in City A?

A) 10%
B) 47%
C) 53%
D) 80%
E) 90%

Question 6

A physical examination,digital rectal exam,was used to screen for prostate cancer in 290 men with biopsy-proven prostate cancer and in 516 age- and race-matched control men,all of whom showed no evidence of cancer at biopsy.The results of the physical examination were positive in 136 cases and in 165 control men.What is the specificity of the physical examination?

A) 32%
B) 47%
C) 53%
D) 68%
E) Cannot calculate it based on given information

Question 7

A physical examination,digital rectal exam,was used to screen for prostate cancer in 290 men with biopsy-proven prostate cancer and in 516 age- and race-matched control men,all of whom showed no evidence of cancer at biopsy.The results of the physical examination were positive in 136 cases and in 165 control men.Now,the health commissioner in City A decides to use a physical exam,digital rectal exam,as a primary screening test for prostate cancer.What will be the positive predictive value of the physical examination?

A) 45%
B) 47%
C) 68%
D) 82%
E) Cannot calculate it based on given information

Question 8

Which of the following statement about positive predictive value is the most accurate?

A) Positive predictive value is a fixed characteristic of the test. It will not change over the person, place, and time.
B) Positive predictive value is affected by the sensitivity of the test only.
C) Specificity will not affect the positive predictive value.
D) Positive predictive value is the probability that a diseased person (case) in the population tested will be identified as diseased by the test.
E) None of above.

Question 9

Mr.Patient tested positive for disease X.He went to see Dr.Gordis and asked him what was the probability of truly being sick given the results of the test.To answer that question,Dr.Gordis must know what about the test?

A) Sensitivity
B) Specificity
C) Prevalence
D) Positive predictive value
E) Negative predictive value

Question 10

The following are problems generated when a patient is given a false-positive diagnosis,except:

A) Generate unnecessary expenses, as those labeled positive often go through other diagnostic procedures.
B) Generates anxiety and worry.
C) Increased burden to the healthcare system
D) The opportunity for an effective intervention is missed.
E) Unnecessary treatments are administered.

Question 11

Which of the following statements about specificity is the most accurate?

A) The probability that a diseased person (case) in the population tested will be identified as diseased by the test.
B) The probability that a person without the disease (noncase) in the population tested will be identified as nondiseased by the test.
C) The probability that a person identified as diseased by the test will be a diseased person (case) in the population.
D) The probability that a person identified as nondiseased by the test will be a person without the disease (noncase) in the population.
E) The probability that a diseased person (case) in the population tested will be identified as nondiseased by the test.

Question 12

A 60-year-old patient was tested for Raven disease; his test came back negative.However,he feels the test might be wrong and wants to know what is the probability of not having Raven disease given that his test came back negative. $$\begin{array}{r}{ \text { Physician 1 } }\quad\quad\\\begin{array} { | l | l | l | } \hline{ \text { Physician } 2 } \\\hline & \text { Positive } & \text { Negative } \\\hline \text { Positive } & 45 & 15 \\\hline \text { Negative } & 25 & 165 \\\hline\end{array}\end{array}$$
Using this table,answer to the following question: what proportion of the patients who tested negative are truly disease free?

A) 4%
B) 33%
C) 66%
D) 70%
E) 96%

Question 13

A diagnostic test with a very high sensitivity but very low specificity has the following problem:

A) It will miss a big proportion of true cases (label them as negatives).
B) It will correctly identify all negative cases.
C) It will label a big proportion of healthy people as sick (false-positives).
D) It will be very expensive to administer.
E) Specificity is the single most important characteristic of a test.

Question 14

A 60-year-old patient,who is an epidemiologist,was tested for Raven disease; his test came back positive.However,he is curious about the sensitivity of the test. $$\begin{array} { | l | c | c | c | } \hline \text { Test } & \text { Disease } ( + ) & \text { No disease } ( - ) & \text { Total } \\\hline \text { Positive } ( + ) & 84 & 44 & 128 \\\hline \text { Negative } ( - ) & 36 & 836 & 872 \\\hline \text { Total } & 120 & 880 & 1,000 \\\hline\end{array}$$
Using this table,calculate the sensitivity of the test.

A) 4%
B) 33%
C) 66%
D) 70%
E) 96%