Homework Questions: Epidemiology

Question 1 is based on the following information:
Two neurologists, Drs. Cortex and Pons, independently examined 130 magnetic resonance images (MRIs) for evidence of astrocytoma (a type of brain tumor). As shown in the table below, the neurologists diagnosed each MRI as either “positive” or “negative” for astrocytoma.

Q1 Based on the above information, the overall percent agreement between Dr. Pons and Dr. Cortex is: (select one)
a. 28.5%
b. 74.0%
c. 80.8%
d. 100%

2. Which of the following is an example of primary prevention? (Select one)
a. Screening apparently healthy people for colorectal cancer using colonoscopies
b. Providing radiation and chemotherapy for treatment of late-stage breast cancer
c. Prescribing daily physical therapy to individuals who have experienced stroke
d. Chlorination of public drinking water to kill bacteria that cause gastrointestinal illness

3. In screening, if people who are screened appear to have better survival outcomes only because the disease was identified earlier, but not because death was delayed, this is what type of bias? (Select one)
a. Recall bias
b. Reporting bias
c. Bias due to length-based sampling
d. Lead time bias

4. Which of the following refers to how well a health service program or intervention works under “real world” conditions? (Select one)
a. External validity
b. Effectiveness
c. Efficacy
d. Internal validity

Question 5 is based on the following abstract:
Objectives. This study aimed to clarify the relationship between community water fluoridation (CWF) and intelligence (IQ) in New Zealand.
Methods. We conducted a study of a general population sample of those born in Dunedin, New Zealand, between April 1, 1972, and March 30, 1973 (95.4% retention after 38 years of follow-up). Residence in a CWF area, use of fluoride dentifrice and intake of 0.5-milligram fluoride tablets were assessed in early life (prior to age 5 years); we assessed IQ repeatedly between ages 7 to 13 years and at age 38 years.
Results. No clear differences in IQ because of fluoride exposure were noted. These findings held after adjusting for potential confounding variables, including sex, socioeconomic status, breastfeeding, and birth weight (as well as educational attainment for adult IQ outcomes).
Conclusions. These findings do not support the assertion that fluoride in the context of CWF programs is neurotoxic. Associations between very high fluoride exposure and low IQ reported in previous studies may have been affected by confounding, particularly by urban or rural status.

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5. Which epidemiologic study design is described above? (Select one)
a. Prospective cohort study
b. Case-control study
c. Cross-sectional study
d. Clinical trial

Questions 6 and 7 are based on the following:
The table below gives information on Town A and Town B in 2012.
Q6   What is the crude mortality rate in Town A in 2012? (Select one)
a. 8.9 per 100
b. 12.1 per 100
c. 16.4 per 100
d. 2.7 per 100

Q7   Using the direct adjustment method and combined populations of Towns A and B as the standard population, what is the age-adjusted mortality rate in Town A? (Select one)
a. 22.6 per 100
b. 10.9 per 100
c. 15.4 per 100
d. 37.3 per 100

Questions 8 and 9 are based on the following data:
Q8 Findings of a prospective study of 1,283 students at XYZ University
You hypothesize that increased soft drink consumption is associated with a high number of new dental cavities.
Using data from the above table, calculate the relative risk for the association between consuming more than one soft drink per day (versus consuming less than one soft drink per day) and high number of new dental cavities.
Report your answer rounded to the tenths decimal place on your answer sheet. Show your work on your answer sheet. (If no work is shown on your answer sheet, half credit will be deducted from the grading of your response to this question, even if your final answer is correct.)

Q9 Given your hypothesis and your answer to the previous question, you decide to investigate how your research assistant collected the data. After reviewing with your research assistant her logs, you both realize she made a mistake in how she classified the outcome, high vs. low number of new dental cavities. This kind of misclassification is an example of: (Select one)
a. Selection bias
b. Modification bias
c. Confounding bias
d. Information bias

Question 10 is based on the following information:
Q10 Case-control study: Number of participants who did and did not have pancreatic cancer (outcome) by Vitamin E levels (exposure) stratified by age group
Based on the above data, which statement is true for this study? (Select one)
a. Age is a confounder of the relationship between vitamin E and developing pancreatic cancer.
b. Age is an effect modifier of the relationship between vitamin E and pancreatic cancer.
c. Age is neither a confounder nor an effect modifier of the relationship between vitamin E and pancreatic cancer.
d. Not enough information to answer this question

Question 11 and 12 are based on the following information:
The incidence of heart attacks among smokers in a community is 30.0 per 100,000 per year. The incidence of heart attacks among non-smokers in this community is 4.0 per 100,000 per year. The proportion of non-smokers in this community is 75%.
11. What proportion of the risk of heart attacks among smokers can be attributed to smoking? (Select one)
a. 6.5%
b. 26.0%
c. 76.0%
d. 86.7%

12. What proportion of the risk of heart attacks in the total population can be attributed to smoking? (Select one)
a. 21.3%
b. 61.9%
c. 82.2%
d. Cannot be calculated given the information provided.

13. In examining the association between an exposure and outcome, which of the following is true about a confounding variable? (Select one)
a. A confounder is a result of the exposure.
b. A confounder is not a risk factor of the outcome of interest.
c. A confounder alters the observed association between the exposure and outcome.
d. A confounder is not associated with the exposure of interest.

14. To develop Disease Z, an individual must have been exposed to environmental toxin A. Some individuals exposed to environmental toxin A, though, will not develop Disease Z.
Based on the above information, environmental toxin A is ________ for developing Disease Z:
a. Necessary and sufficient
b. Necessary but not sufficient
c. Not necessary and not sufficient
d. Not necessary but sufficient

15. Which of the following is true for sequential testing? (Select one)
a. Net specificity is greater than the specificity of either test alone
b. Net specificity is less than the specificity of either test alone
c. Net specificity is the same as that of the more specific test
d. Net specificity is the same as that of the less specific test

16. Question 16 is based on the following adapted abstract:
Maternal vitamin D deficiency has been suggested to influence fetal and neonatal health. Little is known about vitamin D status in Chinese pregnant women. The purpose of this study was to assess the vitamin D status of pregnant women residing in Beijing in winter and evaluate the impact of maternal factors on serum 25-hydroxyvitamin D [25(OH)D] levels. The study was conducted on 125 healthy pregnant women. For each individual, data concerning pre-pregnancy weight, educational status, use of multivitamins and behavioral factors such as daily duration of computer use, walking and sun exposure were obtained. Serum concentrations of 25(OH)D were measured by enzyme-linked immunosorbent assay. The prevalence of vitamin D deficiency (25(OH)D < 50 nmol/L) was 96.8% and almost half (44.8%) of women were severely vitamin D deficiency (25(OH)D < 25 nmol/L). The concentration of 25(OH)D was lower in women with shorter duration of sun exposure (≤ 0.5 h/day, 25.3 ± 8.9 nmol/L) than that in women with longer duration of sun exposure (> 0.5 h/day; 30.3± 9.5 nmol/L; P = 0.003). Thirty-six women (28.8%) had sun exposure duration ≥ 1.5h/day. The 25(OH)D concentration in these women was 31.5 ± 9.4 nmol/L which was also much lower than the normal level. Women who reported taking a multivitamin supplement had significantly higher 25(OH)D concentrations (32.3 ± 9.5 nmol/L) when compared with non-users (24.9 ± 8.2 nmol/L; P < 0.001). Pregnant women in Beijing are at very high risk of vitamin D deficiency in winter. Duration of sun exposure and the use of multivitamin were the most important determinants for vitamin D status. However, neither prolonging the time of sunlight exposure nor multivitamin supplements can effectively prevent pregnant women from vitamin D deficiency.

Which type of epidemiologic study design is described in the above abstract? (Select one)
a. Clinical trial
b. Ecologic study
c. Cross-sectional study
d. Cohort study

Questions 17 and 18 are based on the article described in: Flawed herpes testing leads to many false positives — and needless suffering
17 Based solely on the article, what is the problem with current testing for herpes using the most widely available test “HerpeSelect”? (Select one)
a. Low sensitivity
b. Low reliability
c. Low negative predictive value
d. Low specificity

18. What would be the best approach to addressing the problem in Question 17? (Select one)
a. Simultaneous testing with two different tests
b. Age-adjustment of the herpes rates in the population
c. Sequential testing with two different tests
d. There is no way to boost the accuracy of herpes testing in this context

19. Internal validity of an epidemiologic study refers to the extent that… (Select one)
a. The study was conducted with robust methods and findings are not likely due to error, bias, confounding
b. The findings of the study are able to be confirmed by other investigators using the same methods
c. The participants in the study are representative of all individuals with the specific outcome of interest
d. The human subjects completed the informed consent process before data collection commenced

20. Number of students by amount of Twitter use (exposure) and satisfaction with life (outcome) in a cross-sectional study of 300 JHU undergraduates
Calculate the prevalence ratio for the association between moderate amount of Twitter use (compared to low amount) and more satisfaction with life. (Select one)
a. 0.18
b. 0.30
c. 0.61
d. 0.78

21. Number of students by amount of Twitter use (exposure) and satisfaction with life (outcome) in a cross-sectional study of 300 JHU undergraduates
Based on the table, the conclusion that Twitter use causes less satisfaction with life is: (Select one)
a. Justified because the risk for being more satisfied with life is less than 1 for both high and moderate amount of Twitter use compared to low amount of Twitter use
b. Justified because the study was conducted among JHU undergraduates who are representative of all undergraduate Twitter users
c. Not justified because a cross-sectional study cannot establish temporality, something that is necessary in order to establish causality
d. Not justified because the relative risks were weak, thus failing the causal guideline of strength of association, something that is necessary in order to establish causality

22. An experimental study was conducted to assess the effect of receiving Drug A alone compared to placebo (no treatment) in people with rheumatoid arthritis (RA) for preventing the worsening of RA symptoms. All participants were observed for the same length of time. The findings of the study are summarized in the below table.
Based on the above data, what is the estimate of the relative risk for association for the relationship between Drug A (vs. placebo) and worsening of RA symptoms? (Select one)
a. 0.29
b. 0.35
c. 1.20
d. 3.44

Questions 23-25 are based on the following information:
Providers at a university student health center in Baltimore noticed an increased number of patients with acute gastroenteritis and fever over a six-day period in December 2014. Investigators from the Baltimore City Health Department were notified, and an epidemiologic investigation was undertaken to determine the cause of the outbreak. Blood and stool samples were collected.
Laboratory data indicated that the organism causing the gastroenteritis was Salmonella. Two hundred students (80 sick and 120 not sick) were interviewed, and many reported having eaten at the Lunchbucket, a soup-salad-sandwich place on campus. Each person was asked whether they had eaten soup, salad, or sandwich, or any combination of the three. Data from the investigation are provided below.

23. What is the cumulative incidence of sickness for individuals who reported eating salad?
(Select one)
a. 65%
b. 39%
c. 41%
d. 29%

24. Which food was most likely contaminated with Salmonella? (Select one)
a. Soup
b. Salad
c. Breadsticks
d. Sandwich

25a
Question 25 is based on the following additional information
Patients reported onset of illness during the following days:
Based on data in the above table, what is the median incubation period for this epidemic? (Select one)
a. 5 days
b. 2 days
c. 3 days
d. 4 days