Week 10

Which of the following conditions are favorable to population screening for presymptomatic diagnosis of a given disease? A. A relatively high prevalence of the disease, availability of effective treatment, and a screening test with a high degree of sensitivity B. Availability of physicians to perform the screening test procedure, a screening test with a high degree of sensitivity, availability of effective treatment, and a relatively high prevalence of the disease C. A screening test with a high degree of sensitivity and a relatively high prevalence of the disease D. Availability of effective treatment and availability of physicians to perform the screening test procedure E. Availability of physicians to perform the screening test procedure

A. A relatively high prevalence of the disease, availability of effective treatment, and a screening test with a high degree of sensitivity

A new blood test has been developed to screen for disease Z. Researchers establish 50 unites as a cut point above which test is considered positive and thereby indicative of disease. The test manufacturers are not concerned with the specificity, and they do not want the cost of the test to rise. How can they improve the sensitivity of the test? A. Lower the cut point below 50 units B. Raise the cut point above 50 units C. Test each person's blood twice D. They cannot improve this test and should begin work developing a new test

A. Lower the cut point below 50 units

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? A. The prevalence of virus X infection is higher among the hospital patients than among blood donors B. Measurement error was introduced into the procedure C. Lead time bias occurs among the blood donors D. Cases of virus X infection are more severe in the hospital

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

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 here: Disease Present Disease Absent Positive for Factor X 40 60 Negative for Factor X 10 140 The specificity of this test is expressed as: A. 80% B. 70% C. 56% D. 7% E. 30%

B. 70%

A new screening 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%) The number of false positives is: A. 12 B. 81 C. 99 D. 9 E. 2162

B. 81

Figure 11-12 represents different combinations and qualifies of validity and reliability (high vs. low). Which set of symbols represents low validity a Reliable, invalid b Unreliable, invalid c Reliable, valid A. A B. B C. C

B. B

A test that determines whether disease is actually present is a: A. screening test B. Diagnostic test C. Reliability test D. Validity test

B. Diagnostic test

Sensitivity and specificity of a screening test refer to its: A. reliability B. validity C. yield D. repeatedly

B. validity

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 implemeneted. (Assume the true prevalence of Lyme disease among clinic attendees is 10%) The predicitive value of a positive test is: A. 22.2% B. 33.0% C. 18.2% D. 6.0% E. 94.0%

C. 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 here: Disease Present Disease Absent Positive for Factor X 40 60 Negative for Factor X 10 140 The sensitivity of this test is expressed as: A. 56% B. 30% C. 80% D. 70% E. 7%

C. 80%

Figure 11-12 represents different combinations and qualifies of validity and reliability (high vs. low). Which set of symbols represents high validity a Reliable, invalid b Unreliable, invalid c Reliable, valid A. A B. B C. C

C. C

The degree of agreement among several trained experts refers to: A. Both internal consistency and concurrent validity B. Concurrent validity C. Interjudge reliability D. Internal consistency E. Repeated measure

C. Interjudge reliability

A test developed to assess age-related changes in bone density that does not pick up these changes has: A. Low predictive validity B. Low concurrent validity C. Low construct validity

C. Low construct validity

Lead time bias is best described as: A. an actually longer survival time for persons identified during a screening program because they were given an effective treatment B. an apparently lower survival rate among persons screened compared to an unscreened group C. an apparently longer survival time among persons identified during a screening program because they were identified at an earlier stage of their disease D. a similar survival time for persons identified during a screening program relative to persons who are diagnosed by clinical symptoms

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

Which of the following are the adverse consequences of using a screening test that has a low specificity? A. Failure to identify persons who have the condition B. Increasing the number of persons who are classified as abnormal and necessarily subjecting people to potential risks associated with diagnostic procedures C. Failure to identify persons who have the condition, increasing the number of persons who are classified as abnormal, over referral of persons without disease for diagnosis, and unnecessarily subjecting people to potential risks associated with diagnostic procedures D. Overreferal of persons without disease for diagnosis and failure to identify persons who have the condition E. Unnecessarily subjecting people to potential risks associated with diagnostic procedures, overreferal of persons without disease for diagnosis, and increasing the number of persons who are classified as abnormal

E. Unnecessarily subjecting people to potential risks associated with diagnostic procedures, overreferal of persons without disease for diagnosis, and increasing the number of persons who are classified as abnormal

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

False

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? Specificity refers to the ability of a screening test to identify only non diseased 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

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

True