Ans 1) (d) The exposed and nonexposed groups under study be as similar as possible.
Rationale: Option a is wrong as it is not necessary to have equal number of people in the study groups on whom cohort study is being conducted. Since in this study the occurrence of a disease is calculated discretely and is then standardized by selecting the total population. Option b gets ruled out because we know that a cohort study is disturbed with the presence of new occurrence of the disease after the knowledge of an alleged issue. Option c is even incorrect. It is not a necessity that the study groups should be a representation of the general population. Hence, we are left with Option d.
Ans 2) (a) It usually costs less than a case-control study
Rationale: The cost involved to carry out a future cohort study will typically be more than the cost involved in carrying out a case-control study. This is due to the fact that the former study required a larger number of study groups and hence it lasts longer. As the study groups are generally made distinct because of their exposure status that we can precisely measure them during our studies. As the selected subjects are basically free from diseases at the start which makes it easier to measure their incidence rates as well. Prospective cohort studies, because of its design helps to generate multiple outcomes and exposures, that can be calculated simultaneously.
Ans 3) (c) The required sample size is smaller than that needed for a prospective cohort study.
Rationale: Prospective cohort studies is quite similar in many ways to a retrospective cohort; there exist only a single difference that is: in a retrospective cohort study, there is a use of historical records for gathering data related to the study groups whereas in prospective cohort study the groups are studied longitudinally. Options a, b, and e, in general are majorly the basic characteristics of cohort studies.
Ans 4) (a) The possibility that a factor that led to the exposure, rather than the exposure itself, might have caused the disease.
Rationale: Option A comes out to be the best choice among all the other choices and this has been based on the points mentioned in the textbook, which is “In a nonrandomized study, when we observe an association of exposure with a disease, we are left with uncertainty as to whether the association may be a result of the fact that people were not randomized to the exposure; perhaps it is not the exposure, but rather the factors that led people to be exposed, that are associated with the disease.” Other options like b and c are basically wrong so we know that in a cohort study, group sizes need not be same. Option d is not correct because we are aware that the length of the study is extra reliant on the agent than on its randomization position. Option e is not at all correct as the exposure position of all the study groups are fixed and is not expected to alter.
Ans 5) (c) A number of exposures can be studied simultaneously.
Rationale: Option a is clearly not correct as we know that the population which has to be studied cannot be defined before the exposure as it could lead to extra steps in our study as it would therefore affect the time required for completion of our study. Option b is inappropriate as simultaneously we can study multiple outcomes irrespective of the selection of starting point in the study. Option d is incorrect as we increase the steps in our design, cost would increase as resources would increase. This leaves us with only option c and hence it is the best choice.
Ans 1) (c) Incidence rates may be computed directly
Rationale: Occurrence cannot be computed directly as the design of our study is built on the evaluation of diseased (case) and non-diseased (control) groups where the size of the population is at the choice of the investigator. We know that the cost to carry out a case-control study is typically less as it requires low amount of resources. As the name advocates, in a case-control study we compare the diseased which are called cases with the non-diseased who are called the controls. Calculation of historical exposures may be prejudiced, thus making a key limitation of this design of study. Option e also presents us with an issue concerning the flaws in the design of the study.
Ans 2) (a) A cross-sectional study
Rationale: The crucial characteristic of the cross-sectional study is that we determine simultaneously both the outcome as well as the disease exposure. Here we see that all the residents who were present have been assessed, their exposure level as well as their disease outcomes have been identified individually. Then we compared the ratio of cases vs non-cases.
Ans 3) (b) Obtaining histories and other information from a group of known cases and from a comparison group to determine the relative frequency of a characteristic or exposure under study
Rationale: We know that case-control studies are principally concerned with discovering the multiple cause/causes of disease rather than guesstimating future incidences. Here the study typically starts with identified cases of the ailment consequences, which must be evaluated and the choice of a representative in the risk control group also needs to be identified. Since the starting point is known, the pasts and other data that is composed from each study group is used to limit the frequency of an exposing representative, or the other inducing feature, in each group. The incidence of each group is then equated to analyze whether a causal affiliation exists between the disease consequence and experience(s) under study
Ans 4) (b) A prospective cohort study
Rationale: The above study basically looks like the prospective cohort study. Some of the reasons include, firstly in the start of the study we are made aware that we are dealing with group of individuals belonging to a specific set of population. Secondly, we know that several exposure groups are being formed by dividing the population. For instance, her we see that,3,000 residents of Baltimore were employed in 1965 and classified rendering to alcohol consumption patterns. Third and final is that the groups have been studied over time in order to determine the formation of cancerous cells.
Ans 5) (c) Case-control study
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