Ch 11 notes

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: The sensitivity of this test is expressed as Pos for X and disease present= 40 neg for x disease disease present=10 Pos for x but disease not present= Neg for disease but its there=60 neg for disease and negative for =140

(0.8) 40/ 40+10 sensitivity is the true pos

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: ***see other question The specificity of this test is expressed as:

0.7

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

81

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 test that determines whether disease is actually present is a: A. screening test B. diagnostic test C. reliability test D. none of the above

B- diagnostic test

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%.) The predictive 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/a+b

It is possible for a measure to be valid but unreliable. T/F

F

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 they do not want the cost of the test to rise. How can they improve the sensitivity of the test? Question 18

Lower the cut point below 50 units.

Reliability refers to the ability of a measuring instrument to give consistent results on repeated trials, regardless of its accuracy. T/F

T

Sensitivity refers to the ability of a screening test to correctly identify all screened individuals who have a disease. T/F

T

Specificity refers to the ability of a screening test to identify only nondiseased individuals who actually do not have the disease. (T/F)

T

Validity is the ability of a measuring instrument to give a true measure. T/F

T

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

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) 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? i. unnecessarily subjecting people to potential risks associated with diagnostic procedures ii. overreferral of persons without disease for diagnosis iii. increasing the number of persons who are classified as abnormal iv. failure to identify persons who have the condition. Which of the above statements are correct? A. i, ii., and iii. only B. i and iii. only C. ii and iv. only D. iv only E. i, ii., iii., and iv.

i, ii., and iii. only

What image shows high validity?

in the center and clustered

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

low construct validity

Figure 11-12 represents different combinations and qualities of validity and reliability (high vs. low). Which set of symbols represents low reliability?

spread all over board

Sensitivity and specificity of a screening test refer to its:

validity