Incidence of Coronary Heart Disease (CHD) in Men, According to Initial Cholesterol Level, Followed Over a 10 Year Period (1985-1995) CHD incidence (per 1,000 men) Cholesterol level in 1985 (mg/dL) 300 40 80 140
2. The data in the above table have been obtained from a: (2 pts) A. Case-control study B. Cohort study C. Cross sectional study D. Ecological study E. Cannot be determined from these data
3. The relative risk (RR) of coronary heart disease for men in the highest cholesterol group compared to the lowest group is: (3 pts) A. 140 – 40 = 100 per 1,000 B. 40/140 = 0.29 C. 140/40 = 3.50 D. Cannot be determined from these data
4. If there were no association between an exposure and disease, one would expect the following: (2 pts) A. Relative risk = 1.0 ; Proportion attributable risk = 1.0 B. Relative risk < 1.0 ; Proportion attributable risk < 50% C. Relative risk > 1.1; Proportion attributable risk > 50% D. Relative risk = 1.0; Proportion attributable risk = 0%
5. When a new treatment is developed which prevents death but does not result in the recovery from a non-infectious disease, which of the following will occur? (3 pts) A. Incidence of the disease will decrease B. Prevalence of the disease will increase C. Prevalence of the disease will decrease D. Both the incidence and the prevalence of the disease will increase
6. From January 1988 until March 1990 a research group in New Zealand followed 2,607 infants from the day they were born. Mothers were asked, “What position does your baby usually sleep in?” Mothers of 830 infants reported that their baby slept prone (on its stomach). Among this group, there were 9 infant deaths from Sudden Infant Death Syndrome (SIDS). The remaining 1,777 mothers reported that their baby slept on its side or its back. Among this group, there were 6 deaths from SIDS.
a. What type of study is this? (2 pts)
b. Construct a 2 x 2 table for these data. (4 pts)
c. Calculate the appropriate measure of association and state in words what this number means (one sentence). Show calculations. (6 pts)
7. Are the following examples of incidence or prevalence? Please put your answers under each example. (2 pts each) a. “Rates [of pancreatic cancer] increase rapidly with age as seen in data from the United States, where the rates for patients ages 70–74 are about 57 per 100,000 per year compared to rates of 9.8 per 100,000 in patients age 50–54.” (Lowenfels and Maisonneuve, 2006, p. 200.)
b. “Nearly 5 million asthma sufferers are under age 18. It is the most common chronic childhood disease, affecting more than one child in 20.” (Morbidity and Mortality Weekly Report, NCHS, U.S. CDC, 2003.)
c. Over the past five years, 350 cases of over-worked graduate students have been diagnosed at Drexel University.
8. Match the appropriate sequence of data collection (1-3) with each study design listed below (i.e., for each study design, fill in 1, 2 or 3). (2 pts each)
1. Determine exposure status first, and then collect disease status information. 2. Determine disease status first, and then collect exposure history information. 3. Determine disease status and exposure status at the same point in time.
____ Cross-Sectional Study ____ Cohort Study ____ Case Control Study
9. Match the following strengths to the appropriate study design: (2 pts each) a. Investigation of multiple exposures ____ Case Series b. Investigation of new or emerging diseases ____ Cohort c. Investigator assigns exposure ____ Randomized Clinical Trials d. Ability to calculate incidence rates ____ Case-Control
10. You are conducting a prospective study of hepatitis B virus (HBV) infection and its relation to liver failure. Normally, the immune system neutralizes the virus and most infected people are left with HBV antibodies but no detectable circulating virus. A small proportion of people who are infected with HBV remain with circulating virus itself (HBV viremic) and it is this group that is believed to be at high risk of liver failure. You put together a cohort study of 500 persons who are HBV viremic and 500 persons with HBV antibodies but who do not have detectable virus. You follow this cohort for five years. Among the first group that are HBV viremic, 50 persons develop liver failure: 5 at 10 months, 10 at 20 months, 20 at 36 months, 10 at 42 months, and 5 at 50 months. Among the second group that are HBV antibody positive but who do not have detectable virus (i.e., HBV non-viremic), 10 persons develop liver failure: 5 at 32 months and 5 at 55 months.
a. Calculate the person-time of follow up for each group. Show calculations. (6 pts)
b. Calculate the liver failure incidence rate for each group (i.e., HBV viremic and HBV non-viremic). Express each rate with an appropriate metric in the denominators. Show calculations. (6 pts)
c. How much of an increase of liver failure incidence is seen among persons with detectable HBV virus compared with those who have HBV antibodies but no detectable virus? Give results for absolute and relative differences of incidence. Show calculations. (6 pts)
d. Interpret each measure calculated in 10c above (one sentence each). (6 pts)
11. Which of the following is an appropriate measure of association for a cross-sectional study? (2 pts) a. Incidence rate ratio b. Prevalence ratio c. Cumulative incidence ratio d. Risk difference
12. A relative risk of 1.0 is interpreted as: (2 pts) a. A protective association between the exposure and the disease b. A weak or moderate positive association between the exposure and the disease c. No association between the exposure and the disease d. Cannot be determined without knowing the specific exposure and the disease
13. Why do we age-standardize (age-adjust) incidence data to compare disease incidence between two different populations? Explain and give an example. (6 pts)
14. The tables below come from a case-control study of cervical cancer and test results for exposure to human papilloma virus (HPV).
Cervical Cancer No Cervical Cancer HPV positive 120 18 HPV negative 70 41
After stratifying the above data by smoking status, the following tables were obtained:
Cervical Cancer No Cervical Cancer Smokers HPV positive 100 10 HPV negative 25 5
Cervical Cancer No Cervical Cancer Non Smokers HPV positive 20 8 HPV negative 45 36
a. Before stratifying on smoking behavior, what is the overall odds ratio (OR) found by the study? (3 pts) A. 2.0 B. 1.4 C. 1.0 D. 3.9 E. Cannot be determined from these data.
c. What is the odds ratio for HPV exposure and cervical cancer among smokers only? (3 pts) A. 2.0 B. 1.4 C. 1.0 D. 3.9 E. Cannot be determined from these data.
b. Based on the data above, which statement describes the relationship between cervical cancer and HPV? (3 pts) A. Cervical cancer cases are more likely than controls to have been exposed to HPV. B. When stratified by smoking status, cervical cancer is not associated with HPV in either stratum. C. When stratified by smoking status, there is a stronger association between cervical cancer and HPV in smokers than in non-smokers. D. Cervical cancer is not associated with HPV. E. A cohort study must be done in order to describe the relationship.
15. Disease-specific mortality rates can give a good estimate of the incidence of the disease when the following condition is true: (3 pts) A. The prevalence of the disease is high and duration of disease is short B. The incidence of the disease is high and duration of disease is short C. The mortality rates are age-adjusted D. The case-fatality rate is high and the duration of disease is short E. The crude mortality rate equals the age-adjusted mortality rate
16. The strength of an association is one of the criteria for evaluating the cause and effect relationship between an exposure and outcome. Which of the following is a measure of the strength of association? (2 pts) A. Incidence rate among the exposed B. Cumulative incidence among the exposed C. The ratio of odds of exposure among cases to the odds of exposure among the non-cases D. Odds of disease among exposed relative to the prevalence of exposure in the source population E. None of the above
17. In 2002, investigators started a study of the association of cholesterol levels and stroke in a group of 2,000 healthy persons who had participated in a cholesterol screening program in 1992. The investigators determined exposure categories using cholesterol levels in all persons that were measured at the time of the screening program. A cut-off value of 200 mg/dL was used to define ‘high’ cholesterol while those with levels below 200 were identified as having ‘low’ cholesterol. Using this definition, 1,000 persons had ‘high’ cholesterol levels while the remaining 1,000 persons had ‘low’ cholesterol. The investigators then ascertained whether these originally healthy persons had experienced a stroke. They determined that 150 cases of stroke occurred by the end of 2002, with 113 cases occurring in the high cholesterol group.
a. What is the study design that the investigators used? (2 pts) A. Case-control study B. Retrospective cohort study C. Prospective cohort study D. Cross-sectional study E. Randomized clinical trial
b. What type of measure of association should the investigators calculate? (2 pts) A. Odds ratio B. Prevalence C. Case-fatality rate D. Prevalence ratio E. Relative risk
c. Using the reported study data, what is the association measure that should be calculated? (3 pts) A. 3.1 B. 3.3 C. 67% D. 1.0 E. 0.3
18. The two major purposes of random assignment in a clinical trial are to (select two): (4 pts) A. ensure that study subjects are representative of the general population B. facilitate double-blinding C. ensure that the study groups are comparable on baseline characteristics D. facilitate measurement of outcome variables E. reduce selection bias in allocation of treatment
19. The prevalence of a disease is two times greater in women than in men, but the incidence rates are the same in men and women. Which of the following statements may best explain this situation? (3 pts) A. The duration of the disease is shorter in women. B. The case-fatality rate is lower in women. C. The prevalence of risk factors for developing the disease is greater in men. D. The age-adjusted mortality rate is higher in women. E. The life-expectancy following disease diagnosis is shorter in women.
20. If Disease A has an incidence rate of 17 cases per 100,000 per year and an average duration of 3 years, how many existing cases of the disease will be found in a population of 200,000 people? (3 pts) A. 17 cases B. 34 cases C. 51 cases D. 102 cases E. Cannot be determined from these data
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