PH 630HW CH9_10 - PH 630 Epidemiology Ch. 9 & 10 Homework...

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Chapter 9: #1-5 1) In cohort studies of the role of a suspected factor in the etiology of a disease, it is essential that: Ans.: (d) The exposed and nonexposed groups under study be as similar as possible. Justification : Answer a is incorrect because a cohort study does not require both study groups to have equal numbers or persons; in fact, the design can have more than two study groups. The number of people in each group does not have to be equal, because in a cohort study the incidence of the disease is calculated for each study group separately and incidence is standardized by the total population of each group. Answer b is incorrect also because cohort studies are concerned with the number of new cases (incidence) of a disease that develop after exposure to a suspected factor and therefore subjects must be disease free at inception. So it's the other way around, the group is based on exposure vs nonexposure to a suspected factor and the risk of developing the disease (or not) is studied. Answer c is also incorrect. The study groups do not have to be representative of the general population; the population that the groups are chosen from can be age/sex-specific, or based on some other susceptibility category. In order to control for confounders it would be best to make the groups being studied as similar to each other as possible. 2) Which of the following is not an advantage of a prospective cohort study? Ans.: (a) It usually costs less than a case-control study Justification : A prospective cohort study would typically cost more than a case- control study because it usually requires a larger study group and lasts longer because subjects are studied longitudinally. Precise measurements of exposure are possible because the study groups are defined by exposure status and those assigned to each study group are from a defined population that was selected and followed beforehand. The incidence rates can also be calculated because the subjects selected were disease-free at the beginning of the study and the number new cases are then recorded. Recall bias is less likely because subjects are selected pre-exposure status and followed through to disease development/non- development, whereas a case-control study begins with study groups that are defined by disease status and the exposure status of the subjects in each group is then determined, typically based on self-reported accounts; subjects with the disease are more likely to be driven to recall certain events that those without may not have noticed, or have forgotten. Due to its design, prospective cohort studies allow for many disease outcomes, as well as multiple exposures, to be studied simultaneously. 3)
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This note was uploaded on 12/05/2011 for the course POLISCI 101 taught by Professor Laraja during the Spring '08 term at UMass (Amherst).

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PH 630HW CH9_10 - PH 630 Epidemiology Ch. 9 & 10 Homework...

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