Chapter 11

A new screening test for Lyme disease is developed for use in the general population. The sensitivity and specificity of the new test are 60% and 70%, respectively. Three hundred people are screened at a clinic during the first year the new test is implemented. Assume the true prevalence of Lyme disease among clinic attendees is 10%. Calculate the following value The predictive value of a positive test is:

18.2%

A screening examination was performed on 250 persons for Factor X, which is found in disease Y. A definitive diagnosis for disease Y among the 250 persons had been obtained previously. The results are charted below: The specificity of this test is expressed as:

70%

A screening examination was performed on 250 persons for Factor X, which is found in disease Y. A definitive diagnosis for disease Y among the 250 persons had been obtained previously. The results are charted below: The sensitivity of this test is expressed as:

80%

A new screening test for Lyme disease is developed for use in the general population. The sensitivity and specificity of the new test are 60% and 70%, respectively. Three hundred people are screened at a clinic during the first year the new test is implemented. Assume the true prevalence of Lyme disease among clinic attendees is 10%. Calculate the following valueThe number of false positives is:

81

Figure 4-12 on page 420 represents different combinations and qualities of validity and reliability (high vs. low). Which set of symbols represents low reliability? - A = reliability, invalid - B = unreliable, invalid - C = reliability, valid - Both A and C - None of the above

B

Figure 4-12 on page 420 represents different combinations and qualities of validity and reliability (high vs. low). Which set of symbols represents high reliability? - A = reliability, invalid - B = unreliable, invalid - C = reliability, valid - Both A and C - None of the above

Both A and C

Figure 4-12 on page 420 represents different combinations and qualities of validity and reliability (high vs. low). Which set of symbols represents high validity? - A = reliability, invalid - B = unreliable, invalid - C = reliability, valid - Both A and C - None of the above

C

The degree of agreement among several trained experts refers to:

D - inter-judge reliability

True or False? It is possible for a measure to be valid but unreliable.

False

A new blood test has been developed to screen for disease Z. Researchers establish 50 units as a cut point above which a test is considered positive and thereby indicative of disease. The test manufacturers determine that the test's sensitivity is unacceptably low. However, the manufacturers are not concerned with the specificity and do not want the cost of the test to rise. How can they improve the sensitivity of the test?

Lower the cut point below 50 units.

Drs. Poke and Jab (2014) conducted an employee health program that used 5 screening tests at the same time to detect diseases among workers. Which type of program is this?

Multiphasic screening

Figure 4-12 on page 420 represents different combinations and qualities of validity and reliability (high vs. low). Which set of symbols represents high validity but low reliability? - A = reliability, invalid - B = unreliable, invalid - C = reliability, valid - Both A and C - None of the above

None of the above

A new antibody test detects serum antibodies against virus X (sensitivity 99%, specificity 90%). When applied in a group of hospitalized patients diagnosed as having virus X infections, the test is found to have a positive predictive value of 85%. When used to screen a group of healthy blood donors for virus X infections, the test is found to have a positive predictive value of 30%. Which of the following best explains this difference between the positive predictive values?

The prevalence of virus X infection is higher among the hospital patients than among blood donors

True or False? Reliability refers to the ability of a measuring instrument to give consistent results on repeated trials, regardless of its accuracy.

True

True or False? Sensitivity refers to the ability of a screening test to correctly identify all screened individuals who have a disease.

True

True or False? Specificity refers to the ability of a screening test to identify only nondiseased individuals who actually do not have the disease.

True

True or False? Validity is the ability of a measuring instrument to give a true measure.

True

Lead time bias is best described as:

an apparently longer survival time among persons identified during a screening program because they were identified at an earlier stage of their disease

A test that determines whether disease is actually present is a:

diagnostic test

The adverse consequences of using a screening test that has a low specificity include:i. unnecessarily subjecting people to potential risks associated with diagnostic proceduresii. overreferral of persons without disease for diagnosisiii. increasing the number of persons who are classified as abnormaliv. failure to identify persons who have the condition Which of the above statements are correct?

i., ii., and iii. Only

The conditions favorable to population screening for pre-symptomatic diagnosis of a given disease include:i. a relatively high prevalence of the disease.ii. availability of effective treatment.iii. a screening test with a high degree of sensitivity.iv. availability of physicians to perform the screening test procedure. Which of the above statements are correct?

i., ii., and iii. Only

Choose the best answer. A test developed to assess age-related changes in bone density that does not pick up these changes has:

low construct validity

Sensitivity and specificity of a screening test refer to its:

validity