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A new real time-PCR test for the hepatitis C virus is approved for medical use. The manufacturer sets the threshold number of DNA copies required to achieve a positive result such that the sensitivity is 98% and the specificity is 80%. The tested population has a hepatitis C prevalence of 0.7%. Which of the following changes in the prevalence, incidence, or threshold concentration will increase the positive predictive value of the test, if the other two values are held constant?
An increase in incidence
An increase in prevalence
A decrease in incidence
A decrease in prevalence
Lowering the threshold concentration required for a positive test.
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An at-home recreational drug screening test kit is currently being developed. They consult you for assistance with determining an ideal cut-off point for the level of the serum marker in the test kit. This cut-off point will determine what level of serum marker is associated with a positive or negative test, with serum marker levels greater than the cut-off point indicative of a positive test and vice-versa. The cut-off level is initially set at 4 mg/uL, which is associated with a sensitivity of 92% and a specificity of 97%. How will the sensitivity and specificity of the test change if the cut-off level is raised to 6 mg/uL?
Sensitivity decreases, specificity decreases
Sensitivity increases, specificity decreases
Sensitivity decreases, specificity increases
Sensitivity increases, specificity increases
Sensitivity decreases, specificity may increase or decrease
A 16-year-old female is seen at her outpatient primary medical doctor's office complaining of a sore throat. Further history reveals that she has no cough and physical exam is notable for tonsillar exudates. Vitals in the office reveal HR 88, RR 16, and T 102.1. Using the Centor criteria for determining likelihood of Group A beta-hemolytic strep pharyngitis, the patient has a score of 3. A review of the primary literature yields the findings in Image A. What is the specificity of the Centor criteria using a score of 3 as a cutoff value?
9/54 = 17%
41/50 = 82%
41/46 = 89%
45/50 = 90%
Not enough information has been provided
Health officials are considering a change be made to the interpretation of the tuberculin skin test that will change the cut-off for a positive purified protein derivative (PPD) from 10 mm to 5 mm for healthcare workers. Which of the following is a true statement regarding this potential change?
This change will decrease the positive predictive value of the test
This change will decrease the negative predictive value of the test
This change will not change the negative predictive value of the test
This change will not change the sensitivity of the test
This change will increase the specificity of the test
As a public health practitioner, you are charged with choosing which blood test to use for the screening of a new infectious disease. You want to ensure that as many cases of this disease as possible are picked up by this initial screening test. Which of the following is the highest priority characteristic of this new test?
Highly sensitive test
Highly specific test
Low false positive rate
High true positive rate
Low negative predictive value