Screening: Concepts
Which of the following is NOT one of Wilson & Jungner's screening criteria?
a) Treatment at an early stage should be more beneficial than at a later stage
b) There should be a detectable late stage
c) The test should be acceptable to the patient
d) The costs should be balanced against the benefits
Answer: B (should be "detectable early stage")
Match the type of study to the following definition:
Incidence of disease compared between risk factor groups that are followed over time.
A. Clinical Trial
B. Ecologic
C. Cross Sectional
D. Prospective Cohort
E. Retrospective Cohort
Answer: D and E
In one sentence, interpret the population attributable risk percent (PopAR%) of 46.95% for dental caries.
A. If a high sugar diet were eliminated from this population, one would expect the overall incidence of dental caries in this population to fall by 46.95%.
B. Assuming the association is causal, 46.95% of people with a high sugar diet developed dental caries as a result of their high sugar diet.
C. Assuming the association is causal, 53.05% of people with a high sugar diet developed dental caries as a result of their high sugar diet.
D. A. If a high sugar diet were eliminated from this population, one would expect the overall incidence of dental caries in this population to fall by 53.05%.
Answer: A
Consider an introduction to epidemiology class with 150 enrolled students. None of the students were ill at the beginning of the school year. On September 26, 10 students reported having norovirus. All continued to be ill on October 1, but all 10 recovered within 3 days (by Oct 4th). On October 14, 12 more students developed norovirus. All of these students continued to be ill on October 15, but all but 1 recovered 5 days later (by Oct 20th). The final person continued to be ill until mid-November. In this example, assume that a person cannot get norovirus more than once.
Calculate the cumulative incidence (per 100 students) of norovirus in the class during the month of October.
A. 8.0 per 100 students
B. 8.57 per 100 students
C. 6.67 per 100 students
D. 0.67 per 100 students
Answer: B
12/ (150-10) = 12/140 * 100 = 8.57 per 100 students
When the relation between exposure and disease is different for those who participate in a study and those who do not participate in the study, the following form of bias exists:
A. Information bias
B. Selection bias
C. Confounding
D. Length Bias
Answer: B
Which of these following relationships are not possible?
a) Reliable, but invalid
b) Unreliable and invalid
c) Reliable and valid
d) Valid, but unreliable
Answer: D, not possible to be valid, but unreliable
Match the type of study to the following definition:
Aggregate data (population frequencies) of potential risk factors and outcomes compared at a single
point in time.
A. Clinical Trial
B. Ecologic
C. Cross Sectional
D. Prospective Cohort
E. Retrospective Cohort
Answer: B
What is a correct interpretation of a hypothetical odds ratio of 4.3?
a. Those with stomach cancer have 4.3 times the odds of having a proper diet compared those without stomach cancer
b. Those without stomach cancer have 4.3 times the risk of having a poor diet compared to those without stomach cancer.
c. Those without stomach cancer have 4.3 times the risk of having a proper diet compared to those without stomach cancers.
d. Those with stomach cancer have 4.3 times the odds of having a poor diet compared to those without stomach cancer.
Answer: D
Brookline (Comm A) and Allston (CommB) have identical populations (1 million) and identical cause specific mortality rates for severe hypothermia of 20 per 100,000. The crude mortality rate (CMR) of Comm A is 45 per 100,000 and the CMR of Comm B is 26 per 100,000.
What is the proportional mortality ratio for severe hypothermia in Comm A?
A. 20%
B. 26.3%
C. 44%
D. 45%
Answer: C
No. of deaths due to severe hypothermia= (20/100,000) * (1,000,000) = 200 deaths
Community A: (45/100,000) * (1,000,000) = 450 deaths
Community A: PMR = 200/450 = .44 * 100 = 44%
A population of 200 healthy men was followed for the development of testicular cancer. After being followed for 5 years, 50 men developed testicular cancer. Twenty other men were followed for 2 years and then were lost to follow up. The remaining men who never developed the disease were followed for 10 years.
Calculate the number of person-years of observation accrued by this population.
A. 1,340 person-years
B. 250 person-years
C. 1,550 person-years
D. 1,590 person-years
Answer: D
50 * 5 = 250
+ 20 * 2 = 40
+ 130 *10 = 1,300
1,590 person-years
Which of the following are affected by the prevalence of disease? Select all that apply.
a) Sensitivity
b) Specificity
c) PV+
d) PV-
Answer: C and D, sensitivity and specificity are stable. When prevalence falls, PV+ falls and PV- rises
Select the study design that would best answer the following question:
What is the prevalence of periodontal disease among those with ≤ 12 years of education?
A. Clinical Trial
B. Ecologic
C. Cross Sectional
D. Prospective Cohort
E. Retrospective Cohort
Interpret a negative predictive value of 96.5%:
A. 96.5% of those who test negative truly don’t have cervical cancer (are true negatives).
B. 3.5% of those who test negative truly don’t have cervical cancer (are true negatives).
C. Among the screened population, 96.5% of those who do not have cervical cancer were correctly identified as negative.
D. Of those who receive pap smears, 3.5% of those who do not have cervical cancer will correctly identify as negative.
Answer: A
70,000 women were screened for cervical cancer with a screening papsmear. 8,000 women had a positive papsmear result. These 8,000 women underwent a diagnostic biopsy procedure, and 7,200 of them had a negative biopsy indicating that they truly did not have cervical cancer. Among the remaining 62,000 who screened negative, 250 developed clinical signs of and were diagnosed with cervical cancer within the next year, and are assumed to be false negatives to the screen.
Calculate both the sensitivity and specificity of this screening test.
A. Sensitivity: 76.19%, Specificity: 99.6%
B. Sensitivity: 100%, Specificity: 99.6%
C. Sensitivity: 100%, Specificity: 0.04%
D. Sensitivity: 76.19%, Specificity: 89.56%
Answer: D
800/1,050 = 76.19%
61,750/68,950 = 89.56%
Match each with their best data source
1. Number of cases of measles, malaria, and tetanus in the US in 2009
2. Overall mortality rate
3. Rates of anxiety disorder in a county
4. Cancer cases in Connecticut.
A. US Census
B. Vital Statistics
C. Reportable Diseases (CDC)
D. Disease registry
E. Survey
1. C
2. B
3. E
4. D
Which of the following is not a characteristic of a disease appropriate for screening?
a) It's a disease with serious consequences
b) Treatment would be more effective at earlier stages
c) It has a detectable preclinical phase
d) It has a short preclinical phase
Answer: D, instead it should be "a long preclinical phase (>year)"
Select the study design that would best answer the following question:
What is the relationship between the average population consumption of trans-fatty acids and all-cause mortality rates?
A. Clinical Trial
B. Ecologic
C. Cross Sectional
D. Prospective Cohort
E. Retrospective Cohort
Answer: B
Interpret a sensitivity of 92.3% (select all):
A. Among this screened population, 92.3% of breast cancer cases were identified by mammography (tested positive).
B. 92.3% of those who screen positive truly do have breast cancer.
C. Of those who receive mammographies, 7.7% of all true breast cancer cases will be detected.
D. Of those who receive mammographies, 92.3% of all true breast cancer cases will be detected.
Answer: A, D
70,000 women were screened for cervical cancer with a screening papsmear. 8,000 women had a positive papsmear result. These 8,000 women underwent a diagnostic biopsy procedure, and 7,200 of them had a negative biopsy indicating that they truly did not have cervical cancer. Among the remaining 62,000 who screened negative, 250 developed clinical signs of and were diagnosed with cervical cancer within the next year, and are assumed to be false negatives to the screen.
Calculate the negative and positive predictive values of this screening test.
A. PPV: 10%, NPV: 89.56%
B. PPV: 76.19%, NPV: 89.56%
C. PPV: 10%, NPV: 99.6%
D. PPV: 100%, NPV: 99.6%
Answer: C
PPV: 800/8000 = 10%
NPV: 61750/62000 = 99.60%
Atlantis is a city with a population of 5,000,000, made up of 2,700,000 men and 2,300,000 women. In 2012, they reported the following vital statistics:
Number of deaths from all infectious diseases=50,000
Number of deaths from car accidents=15,000
Number of deaths from lung cancer=2,500
Total number of deaths=250,000
Indicate what the crude mortality (death) rate (per 100,000), cause-specific mortality rate (per 100,000) from lung cancer, and proportional mortality ratio for car accidents were.
A. 250,000/5,000,000, 15,000/250,000, 2,500/5,000,000
B. 2,500/5,000,000, 250,000/5,000,000, 15,000/250,000
C. 250,000/5,000,000, 2,500/5,000,000, 15,000/250,000
D. 15,000/250,000, 250,000/5,000,000, 2,500/5,000,000
Answer: C
Researchers considered that poor dietary habits increased one’s chances of developing stomach cancer. A study was designed to test this hypothesis. Investigators identified a group of 1900 patients whose initial diagnosis on admission to hospital was stomach cancer. Another group of 410 patients, admitted to the hospital for non-cancer reasons, were also identified. Then both groups of patients were interviewed regarding their dietary habits. Of those with cancer, 900 of them self-reported poor diet habits and of those without cancer, 345 of them self-reported proper diet habits.
Calculate the RR and OR from a 2x2 table.
A. RR=2.99, OR=1.25
B. RR=1.25, OR=4.78
C. RR=4.78, OR=2.99
D. RR=0.90, OR=4.78
Answer: B
RR=(900/965)/(1000/1345) = 1.25
OR=(900*345)/(65*1000) = 4.78
Match each intervention with the appropriate type of prevention
1. Screening for Tay-Sachs disease in Ashkenazi Jewish population
2. Rehabilitation for stroke patients
3. Fluoridation of drinking water
A. Primary Prevention
B. Secondary Prevention
C. Tertiary Prevention
1. B
2. C
3. A