Practice Questions 2 [Chapter 9-18] Book: Epidemiology [Leon Gordis]

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NUR 527: Fundamentals of Epidemiology

and Biostatistics for Nursing

Practice Questions 2 [Chapter 9-18]
Book: Epidemiology [Leon Gordis]
Due June 24, 2013

Answer only the questions specified and justify your answers.

Each question is “one point”. Total points=20 (10% of the course grade)

Chapter 9: questions 1, 2, 5
1. In cohort studies of the role of a suspected factor in the etiology of a disease, it is essential that: a. There be equal numbers of persons in both study groups b. At the beginning of the study, those with the disease & those without the disease have equal risks of having the factor c. The study group with the factor and the study group without the factor be representative of the general population d. The exposed & nonexposed groups under study be as similar as possible with regard to possible confounding factors e. Both b and c

Answer: D
According to Gordis, “Often, strong evidence does not exist to justify mounting a large and expensive study for indepth investigation of the role of a specific risk factor in the etiology of a disease. Even when such evidence is available, a cohort of exposed and nonexposed persons often cannot be identified. Generally, we do not have appropriate past records or other sources of data that enable us to conduct a retrospective cohort study; as a result, a long study is required because of the need for extended follow-up of the population after exposure”. (pg. 175) The closer the exposed and nonexposed can be the easier it is to identify the causing factors.

2. Which of the following is not an advantage of a prospective cohort study? a. It usually costs less than a case-control study
b. Precise measurement of exposure is possible
c. Incidence rates can be calculated
d. Recall bias is minimized compared with a case-control study e. Many disease outcomes can be studied simultaneously ANSWER: A
According to Gordis, “A major problem with the cohort design just described is that the study population often must be followed up for a long period to determine whether the outcome of interest has developed.” (pg. 170) The longer the study needs to be continued the more expensive it can be. The prospective cohort study needs to be carried out all the way with all participants. A case-control study only those affected need to be studied.

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5. In a cohort study, the advantage of starting by selecting a defined population for study before any of its members become exposed, rather than starting by selecting exposed and non-exposed individuals, is that: a. The study can be completed more rapidly

b. A number of outcomes can be studied simultaneously c. A number of exposures can be studied simultaneously d. The study will cost less to carry out
e. a and d
ANSWER: C
According to Gordis, cohort study, discussed in Chapter 9, which begins with a group of exposed people and compares them to a nonexposed group. Some people have the erroneous impression that the distinction between the two types of study design is that cohort studies go forward in time and case-control studies go backward in time. Such a distinction is not correct; in fact, it is unfortunate that the term retrospective has been used for case-control studies, as the term incorrectly implies that calendar time is the characteristic that distinguishes case-control from cohort design (pg. 179)

Chapter 10: questions 1, 3, 8
1. A case-control study is characterized by all of the following except: a. It is relatively inexpensive compared with most other epidemiology study designs b. Patients with the disease (cases) are compared with persons without the disease (controls) c. Incidence rates may be computed directly

d. Assessment of past exposure may be...
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