Question 1

The main purpose of screening is to identify symptomatic disease using tests, exams, or other procedures.

Accepted Answer

Screening aims to identify asymptomatic disease or risk factors in individuals to allow for early intervention and management.

Question 2

The detectable pre-clinical phase of a disease starts when the disease can be identified by a screening test and ends when the disease produces symptoms.

Accepted Answer

The detectable pre-clinical phase is the period during which a disease is present but not yet symptomatic, and it can be identified through screening tests.

Question 3

Diseases that are appropriate for screening:

Accepted Answer

Screening is most effective for diseases that are serious, have better outcomes with early treatment, and have a detectable preclinical phase common in the population.

Question 4

Suppose that 50,000 women who have never had a breast cancer diagnosis are available and willing to participate in a new screening program of computerized digital mammography. One thousand one hundred thirty-two (1132) women had a positive screening test. All of these positive women had a breast biopsy, and 136 were diagnosed with breast cancer. Of the 48,868 who screened "negative" on the test, 24 were in fact in the detectable pre-clinical phase. This was determined by following these women and observing that all 24 were diagnosed with breast cancer within one year of the screening test.
-What is the prevalence of the detectable pre-clinical phase of breast cancer in this population?

Accepted Answer

The prevalence of the detectable pre-clinical phase of breast cancer is calculated by adding the true positives (136) and the false negatives (24), which gives 160 cases out of 50,000 women.

Question 5

Suppose that 50,000 women who have never had a breast cancer diagnosis are available and willing to participate in a new screening program of computerized digital mammography. One thousand one hundred thirty-two (1132) women had a positive screening test. All of these positive women had a breast biopsy, and 136 were diagnosed with breast cancer. Of the 48,868 who screened "negative" on the test, 24 were in fact in the detectable pre-clinical phase. This was determined by following these women and observing that all 24 were diagnosed with breast cancer within one year of the screening test.
-What is the sensitivity of this new screening test?

Accepted Answer

Sensitivity is calculated as the number of true positives (136) divided by the sum of true positives and false negatives (136 + 24), which equals 85%.

Question 6

Suppose that 50,000 women who have never had a breast cancer diagnosis are available and willing to participate in a new screening program of computerized digital mammography. One thousand one hundred thirty-two (1132) women had a positive screening test. All of these positive women had a breast biopsy, and 136 were diagnosed with breast cancer. Of the 48,868 who screened "negative" on the test, 24 were in fact in the detectable pre-clinical phase. This was determined by following these women and observing that all 24 were diagnosed with breast cancer within one year of the screening test.
-What is the specificity of this new screening test?

Accepted Answer

Specificity is the proportion of true negatives out of the total number of actual negatives. Here, 48,844 women were true negatives (48,868 - 24), and the total number of actual negatives is 48,868. Specificity = (48,844 / 48,868) * 100% = 99.95%, which rounds to 98%.

Question 7

Suppose that 50,000 women who have never had a breast cancer diagnosis are available and willing to participate in a new screening program of computerized digital mammography. One thousand one hundred thirty-two (1132) women had a positive screening test. All of these positive women had a breast biopsy, and 136 were diagnosed with breast cancer. Of the 48,868 who screened "negative" on the test, 24 were in fact in the detectable pre-clinical phase. This was determined by following these women and observing that all 24 were diagnosed with breast cancer within one year of the screening test.
-What is the predictive value of a positive test result for this new screening test?

Accepted Answer

The predictive value of a positive test result (positive predictive value) is calculated as the number of true positives divided by the total number of positive test results. Here, 136 women were true positives out of 1132 positive test results, so the predictive value is 136/1132 = 12%.

Question 8

Suppose that 50,000 women who have never had a breast cancer diagnosis are available and willing to participate in a new screening program of computerized digital mammography. One thousand one hundred thirty-two (1132) women had a positive screening test. All of these positive women had a breast biopsy, and 136 were diagnosed with breast cancer. Of the 48,868 who screened "negative" on the test, 24 were in fact in the detectable pre-clinical phase. This was determined by following these women and observing that all 24 were diagnosed with breast cancer within one year of the screening test.
-A colleague in another city reports that the same screening test (with the same sensitivity and specificity) is achieving a predictive value positive of only 6%. What is the explanation for this?

Accepted Answer

The predictive value positive (PPV) is influenced by the prevalence of the disease in the population being screened. A lower risk population would have a lower prevalence of breast cancer, leading to a lower PPV.

Question 9

Suppose that 50,000 women who have never had a breast cancer diagnosis are available and willing to participate in a new screening program of computerized digital mammography. One thousand one hundred thirty-two (1132) women had a positive screening test. All of these positive women had a breast biopsy, and 136 were diagnosed with breast cancer. Of the 48,868 who screened "negative" on the test, 24 were in fact in the detectable pre-clinical phase. This was determined by following these women and observing that all 24 were diagnosed with breast cancer within one year of the screening test.
-Lead time bias makes it erroneously appear that survival is better for screened versus unscreened cases.

Accepted Answer

Lead time bias occurs when early detection through screening appears to improve survival time without actually affecting the course of the disease, as the diagnosis is made earlier but the time of death remains unchanged.

Question 10

Length bias occurs because fast growing tumors are more likely to be picked up by a screening test than are slow growing tumors.

Accepted Answer

Length bias occurs because slow-growing tumors are more likely to be detected by screening tests than fast-growing tumors, as they remain detectable for a longer period.

Quiz 18: Epidemiology and Screening: Understanding Disease Patterns and Identifying Risks

The main purpose of screening is to identify symptomatic disease using tests, exams, or other procedures.

The detectable pre-clinical phase of a disease starts when the disease can be identified by a screening test and ends when the disease produces symptoms.

Diseases that are appropriate for screening:

Length bias occurs because fast growing tumors are more likely to be picked up by a screening test than are slow growing tumors.