Independent Study for Epidemiology Examination

Questions 1-3 are based on Figure 1.

Figure 1 (attached) is a schematic presentation of disease occurrence over a time period. Each horizontal line represents the disease experience of one individual. The dotted line indicates the time period in which the individual had the disease. There are 20 persons in this population. The vertical line at A is the point at which the point prevalence will be determined.

Q1. What is the numerator for the cumulative incidence of the disease in the group, during the study period?

A. 8

B. 10

C. 12

D. 18

E. 20

Q2. What is the denominator for the cumulative incidence of the disease in the group, during the study period?

A. 8

B.10

C. 12

D.18

E. 20

Q3. What is the prevalence of the disease (per 1000) at point A?

A. 250 / 1000

B. 500 / 1000

C. 556 / 1000

D. 6001 1000

E. 667 / 1000

Questions 4-10 are based on the following scenario:

Recently, a report in the Centers for Disease Control (CDC) publication Morbidity and Mortality Weekly described a string of individual cases of Norwalk virus gastroenteritis occurring on cruise ships. From this report, the editor went on to form a number of hypotheses as to why there has been this rather unusual increase in reported gastroenteritis outbreaks on cruise ships in 2002.

The cruise ship owners contacted the CDC to conduct an in-depth analysis of the possible modes of transmission of the Norwalk virus in the cruise ship environment. CDC investigators interviewed all of the passengers on the last affected cruise (N=3,000) and obtained information on the passenger's recreational activities. They found the following results: 1,000 passengers had gone swimming in the upper deck pool and 2,000 passengers had never gone swimming in the upper deck pool. 100 of the passengers who swam in the upper deck pool and 100 of the passengers who did not swim in this pool developed Norwalk virus gastroenteritis during the cruise. FYI: The cruise lasted one week.

Q4. Set up the two by two table for these data.

Q5. Calculate the risk ratio of gastroenteritis associated with swimming in the upper deck pool.

Q6. State in words your interpretation of the above risk ratio.

Q7. Calculate the risk difference in the above example. Use a base of 1000.

Q8. State in words your interpretation of the above risk difference.

Q9. What measure of association should be used to answer the question, "How many additional cases of Norwalk virus gastroenteritis among all cruise passengers (N=3,000) was associated with swimming in the upper deck pool?"

Q10. When the cruise ship owners examined the findings of the CDC investigation, they stated that the crude results (calculated above) were invalid because of the age differences between the people who swam in the upper deck pool and those who did not. Examine the following table and state whether or not you agree with the cruise ship owners.

a. Based on these data, do you agree or disagree with the assessment that the crude results were invalid? Briefly justify your answer.

b. Regardless of whether you agree with the cruise ship owners, explain i the method that epidemiologists use to account for age differences in populations. Be sure to mention what additional data would be needed to perform this procedure.

Questions 11-13 are based on the following figure:

The attached figure was prepared by the HIV Epidemiology Program of the Los Angeles County Public Health Division. It was published in the HIV/AIDS Semi-Annual Surveillance Report (January 2009).

FIGURE - PERSONS REPORTED LIVING WITH HIV/AIDS AS CIF 12/31/2008 (1) AND LIVING HIV/AIDS RATE (2) PER 100,000 POPULATION BY SERVICE PLANNING AREA (SPA) (3) IN LA COUNTY, (N = 41,803)

Q11. As a member of the HIV Epidemiology Program, which of the following would most likely fit into your job description? (Circle all that apply)

A. Calculate prevalence rates by geographic region

B. Collect HIV/AIDS surveillance data

C. Clinically monitor AIDS treatment regimens

D. Test blood samples for HIV infection

Q12. Based on the figure, which geographic community appears to have the highest number of persons with 1-HWAIDS infections?

A. South Bay

B. South

C. Metro

D. West

Q13. Based on the figure, which geographic community appears to have the second highest HIV/AIDS Rate per 100,000 Population?

A. South Bay

B. South

C. Metro

D. West

Q14. Consider a group of 1,000 newborn infants, 100 infants were born with serious birth defects and 20 of these 100 died during the first year of life. 90 of the 900 remaining infants without any birth defects also died during the first year of life.

a. Calculate the prevalence of serious defects in this population at the time of birth. Use base of 1,000.

b. Calculate the overall cumulative incidence of mortality in this population. Use base of 1,000.

c. Calculate the cumulative incidence difference in mortality between infants born with serious birth defects and without. Use base of 1,000,

d. State in words your interpretation of the cumulative incidence difference calculated in part c.

Q15. A group of 100 healthy women was followed prospectively for 10 years. All subjects entered the study on January 1, 1990 and all women were followed until December 31, 1999. None were lost to follow-up. During this period, 5 subjects were diagnosed with breast cancer, but they all survived to the end of the study. The time at which these 5 subjects developed cancer is shown in this table. Assume that each diagnosis occurred exactly half way through the year.

a. What was the cumulative incidence of breast cancer? Use base of 100.

b. What was the prevalence of breast cancer "survivors" on December 31, 1999? Use base of 100.

Questions 16-20 are based on the following scenario:

In January 2000 you began a one-year study of tuberculosis (TB) in a subsidized housing community in the Lower East Side of New York City. You enrolled 500 residents in your study and checked on their TB status on a monthly basis. At the start of your study on January 15#, you screened all 500 residents. Upon screening, you found that 20 of the healthy residents were immigrants who were vaccinated for TB and so were not at risk. Another 30 residents already bad existing cases of TB on January 1st. On February 1st, 5 residents developed TB. On April 1ST, 5 more residents developed TB. On June is', 10 healthy residents moved away from New York. City were lost to follow-up. On July 1st, 10 of the residents who had existing TB on January 1" died from their disease. The study ended on December 31, 2000_ Assume that once a person gets TB, they have it for the duration of the study, and assume that all remaining residents stayed healthy and were not lost to follow-up.

Q16. Is the subsidized housing community in the Lower East Side of New York City a dynamic or fixed population? Briefly explain the rationale for your answer.

Q17. What was the prevalence of TB in the screened community on January 1^st? Use base of 100.

Q18. What was the prevalence of TB on June 30^th? Use base of 100.

Q19. What was the cumulative incidence of TB over the year? Use base of 100.

Q20. Suppose that you wanted to calculate the incidence rate of TB in the study population. Calculate the amount of person-time that would go in the denominator of this incidence rate.

Questions 21-27 are based on the following information:

A cohort study of coffee drinking and anxiety was conducted at a university campus. There were a total of 30,000 freshmen who participated. 10,000 were coffee drinkers and 20,000 were not. Of the coffee drinkers, 500 developed anxiety during the 4 year follow-up period. Of the non-coffee drinkers, 200 developed anxiety during the same time period. Assume that no one in the population died or was lost during the follow-up period.

Q21. What was the cumulative incidence of anxiety among coffee drinkers?

A. 2.0 % over a four year period.

B. 5.0 % over a four year period.

C. 1.0 % over a four year period.

D. None of the above

Q22. What was the cumulative incidence of anxiety among non-coffee drinkers?

A. 2.0 % over a four year period.

B. 5.0 % over a four year period.

C. 1.0 % over a four year period.

D. None of the above

Q23. Calculate the risk ratio (a.k.a. relative risk) using the given data. The numeric value of the risk ratio

A. 1.0

B. 0.2

C. 5.0

D. None of the above

Q24. Which of the following is the correct interpretation of this risk ratio?

A. Coffee drinkers are "x" times as likely to develop anxiety as compared to non-coffee drinkers.

B. The excess risk of anxiety among coffee drinkers is "x" as compared to non-cofTee drinkers.

C. The excess risk of anxiety among the entire freshmen population is "x".

D. None of the above.

Q25. Calculate the population risk difference using the given data, The numeric value of the population risk difference is

A. 1.3 (per 100)

B. 2.7 (per 100)

C. 3.3 (per 100)

D. None of the above.

Q26. Which of the following is the correct interpretation of the population risk difference?

A. Coffee drinkers are "x" times as likely to develop anxiety as compared to non-coffee drinkers.

B. The excess risk of anxiety among the coffee drinkers is "x"

C. The excess risk of anxiety among the entire freshmen population is "x"

D. None of the above.

Q27. Which measure of association is commonly used by researchers to determine the strength of the relationship between an exposure and disease?

A. Risk/Rate ratio (a.k.a. relative risk)

B. Risk/Rate difference

C. Population risk/rate difference

D. None of the above.

Q28. What would be the effect on the incidence and prevalence of pancreatic cancer if an effective, life-prolonging treatment, but NOT curative, for the disease were developed? (Assume no other new developments. The ease-fatality rate for pancreatic cancer is currently high).

A. both incidence and prevalence would decrease B, both incidence and prevalence would increase

C. incidence would not change, but the prevalence would increase

D. incidence would not change, but the prevalence would decrease

E. prevalence would not change, but incidence would decrease

Q29. How does each of the following conditions influence the prevalence of a disease in a population? For each scenario, assume that no other changes occur. Your choices are: increases prevalence, decreases prevalence, or has no effect on prevalence.

A. A treatment is developed that prolongs the life of people suffering from the disease

B. A new preventative measure is developed that prevents new cases of disease from occurring

C. There is immigration of a large number of healthy people into the population.

Q30. If an exposure has no association with a certain outcome, then what value would you obtain for each of the measures of association listed below?

A. Rate ratio

B. Rate difference

Q31. Which of the following is an example of a "fixed" population?

A. The patient population of Boston Medical Center

B. Spring 2006 graduates of BUSPH

C. The residents of the City of Cambridge

D. The student body of BUSPH

Q32. In 2000, the number of new cases of influenza was 50 in Somerville and 1,075 in Boston. Which city had a higher cumulative incidence of influenza in 2000?

A. Somerville

B. Boston

C. Can't be determined based on the information given

Q33. Quote from a news report: "Based on interviews and blood samples of over 8,000 persons, 11% of persons classified as heavy drinkers of alcohol were involved in home accidents over a three-month period." Can we conclude that there is an association between drinking and home accidents from these data? Circle YES or NO and briefly justify your answer.

Attachment:- Assignment File.rar