Deck 18: Epidemiologic Approach to Evaluating Screening Programs

Question 1

A recent study found that screening for disease X led to increased survival.In the study,those who were screened were generally younger,healthier,and more aware of their health than those who were not screened.This makes it hard to evaluate whether the improvement in survivorship was due to the screening program or due to the characteristics of those who are screened.What is the name of this issue when evaluating the effect of a screening program?

A) Lead time bias
B) Overdiagnosis bias
C) Selection bias
D) Misclassification bias
E) Length-biased sampling

Answer 1

C
Selection bias is an important issue to consider when evaluating the effectiveness of screening programs.Usually,participants of a screening program are healthier than the general population,and therefore it becomes hard to assess whether the screening program was effective or whether the characteristics of those who participate in it make it seem effective.

Question 2

The following is a reason for an apparent lack of benefit from a screening program:

A) The available treatments are not effective even when administered early in the disease progression.
B) The clinical phase of disease is long and usually ends with the death of the patient.
C) The usual diagnosis of disease happens very late in the disease progression.
D) The preclinical phase of disease is very long.
E) The current therapies are very effective when administered in the preclinical phase of disease.

Answer 2

A
Screening programs will be effective only when the available treatments are more effective when administered in the preclinical or early stages in the disease progression.

Question 3

Epidemiologists decided to investigate the validity of new diagnostic tool for breast cancer.They used this new diagnostic tool for breast cancer in 150 women with biopsy-proven breast cancer in 300 age- and race-matched control women.The results of the new tool were positive in 136 cases and in 35 control women,all of whom showed no evidence of cancer at biopsy.Now,the epidemiologists want to use the new diagnostic tool for screening program in Cities A and B.Based on previous cross-sectional studies,the prevalence of breast cancer is 5% in City A and 1% in City B.What is the most reasonable conclusion to be drawn from these data?

A) Positive predictive value of new diagnostic tool for breast cancer in City A is higher than expected positive predictive value in City B.
B) Positive predictive values will be higher than sensitivity.
C) Positive predictive value is affected by the specificity of the test only.
D) Prevalence will not affect the positive predictive value.
E) Positive predictive value is a fixed characteristic of the test. Therefore the positive predictive value in City A will be same as positive predictive value in City B.

Answer 3

A
The sensitivity of new diagnostic test is 91%,from 136 divided by 150.The specificity of new diagnostic test is 89%,from 265 divided by 300.The positive predictive value is the number of people who test positive from people who have cancer divided by total number of people who test positive from people who have cancer and people who do not have cancer,which equals sensitivity multiplied by prevalence divided by addition of sensitivity multiplied by prevalence and 1 minus specificity multiplied by 1 minus prevalence.Therefore the positive predictive value of the test in City A is 0.30,which equals 0.05 multiplied by 0.91 divided by addition of 0.05 multiple 0.91 and 0.11 multiplied by 0.95.The positive predictive value of the test in City A is 0.01,which equals 0.01 multiplied by 0.91 divided by addition of 0.01 multiplied by 0.91 and 0.11 multiplied by 0.99."Positive predictive values will be higher than sensitivity" is not correct.Positive predictive values are lower than sensitivity."Positive predictive value is affected by the specificity of the test only" and "Prevalence will not affect the positive predictive value" are not correct.Positive predictive values are affected by sensitivity,specificity,and prevalence."Positive predictive value is a fixed characteristic of the test.Therefore the positive predictive value in City A will be same as positive predictive value in City B" is not correct; positive predictive value is not a fixed characteristic of the test.

Question 4

In the model of the Natural History of Disease,the period of time between the onset of signs and symptoms of disease and its ultimate outcome (cure,control,or death) is known as

A) preclinical phase.
B) clinical phase.
C) clinical horizon.
D) incubation period.
E) latent period.

Question 5

Which of the following statements is the most accurate example of secondary prevention?

A) Providing human papillomavirus (HPV) vaccines to kids who are 11 or 12 years of age
B) Using condoms to prevent sexually transmitted disease
C) Taking a routine Pap smear test
D) Receiving a hysterectomy after diagnosis of cervical cancer
E) Participating in rehabilitation programs to reduce the pain after surgery

Question 6

Which of the following statements is the most accurate example of primary prevention?

A) Promoting antismoking campaign in the community
B) Taking low-dose computed tomography scan to detect the early stage of lung cancer
C) Quitting smoking after diagnosis of chronic obstructive pulmonary disease
D) Removal of malignant lung cancer to reduce the pain from tumor
E) Participating in cancer rehabilitation programs in primary health care center after surgery

Question 7

Which of the following statements is not an accurate description of epidemiologic studies using large group data such as National Hospital Discharge Survey or National Health Interview Survey?

A) The advantage of using large data sets is that the data refer to real-world populations; the issue of representativeness is minimized.
B) Because the data sets exist at the time the research is initiated, analysis can be completed and results generated relatively rapidly.
C) Given the large data sets used, sample size is usually considered a major problem.
D) Data are usually gathered for fiscal and administrative purposes; they may not be well suited for scientific research.
E) When necessary variables or questions are absent, the investigators may consciously or subconsciously change the research questions.

Question 8

Epidemiologists decided to investigate the validity of new diagnostic tool for breast cancer.They used this new diagnostic tool for breast cancer in 150 women with biopsy-proven breast cancer in 300 age- and race-matched control women.The results of the new tool were positive in 136 cases and in 35 control women,all of whom showed no evidence of cancer at biopsy.Now,the epidemiologists want to use the new diagnostic tool for screening program in Cities A and B.Based on previous cross-sectional studies,the prevalence of breast cancer is 5% in City A and 1% in City B.What is the expected positive predictive value of new diagnosis tool for breast cancer in City A?

A) 30%
B) 43%
C) 81%
D) 89%
E) 91%

Question 9

Which of the following statements is the most accurate example of tertiary prevention?

A) Receiving a yellow fever vaccination at a tertiary hospital
B) Using a mosquito net while visiting a malaria-endemic country
C) Taking preventative malaria drug before getting an infection
D) Receiving regular blood smear test to detect the malaria early
E) Joining malaria rehabilitation programs to reduce or eliminate long-term impairments and disabilities from previous infections

Question 10

The usual time to death after diagnosis of disease X is 2 years.A screening program allows for the early detection of disease X,on average 1 year earlier than the usual diagnosis; however,there is no available treatment even in early stages of disease X.With the screening program it seems like the time to death has increased to 3 years; however,this is only due to the early diagnosis thanks to the screening program.What is the name of the issue previously described?

A) Timing bias
B) Survival bias
C) Selection bias
D) Confounding
E) Lead-time bias

Question 11

In the model of the Natural History of Disease,when is the ideal time to do screening for a disease?

A) Preclinical phase
B) Clinical phase
C) Clinical horizon
D) Before disease starts
E) Latent period

Question 12

Epidemiologists decided to investigate the validity of new diagnostic tool for breast cancer.They used this new diagnostic tool for breast cancer in 150 women with biopsy-proven breast cancer in 300 age- and race-matched control women.The results of the new tool were positive in 136 cases and in 35 control women,all of whom showed no evidence of cancer at biopsy.What is the sensitivity of new diagnosis tool for breast cancer?

A) 9%
B) 12%
C) 33%
D) 91%
E) 88%