Ch. 10 Case-Control Studies and other designs Flashcards
True or False: Comparison is an essential component of epidemiologic investigations and is well exemplified by the case-control study design.
True.
Explain the design of a Case-Control Study.
In order to examine a possible relation to an exposure of to a certain disease the design, we identify individuals with the disease (cases) and those without (controls). Where we determine what proportion of the two groups were exposed and non-exposed of past exposure. This can be done by interviewing, reviewing medical records, employee records, and the results of chemical or biological assays.
a- cases who were exposed
b- cases who were not exposed
c- controls who were exposed
d- controls who were not exposed
How can case participant be selected for the case-control studies? And what factors do you have to keep in mind?
Patients may be obtained through a variety of sources such as a registry, a hospital, a physicians clinic and serve as a valuable source for such studies. Though it is important to keep in mind that the case-control criteria be carefully specified and the selection of individuals from a single hospital or source may be unique to that source.
What considerations must be kept in mind when conducting a case-control study regarding the selection of either incident or prevalent cases?
The decision to use incident (newly) or prevalent cases arises from the problem that we often have to wait for new cases to be diagnosed properly. Thus a large a larger number of prevalent cases are needed and and tend to be available. However, it is preferable to use incidence cases.
Why is it preferable to use incidence cases for a case control study?
The risk factors used when using prevalent cases may be due more to survival with the disease rather than the development of the disease. Though we still run the risk of loosing patients before diagnosis can be made.
Where can controls be selected from?
Controls may be gathered from non-hospitalized persons in the community or from hospitalized patients admitted for diseases other than the cases for which they were admitted.
What approaches are used to gather a number of non hospitalized controls?
3 approaches included: Neighborhood Controls, Digit Dialing Control Model, and the Best Friend Control.w
When using Hospitalized patients as control groups what factors might you keep in mind?
-The question of which diagnostic groups should be included and which would be excluded within the study are unlikely to be representative of the general population and thus should be stated implicitly.
How do we differ the cases and controls when using hospitalized patients in a case-control study?
One approach is to not exclude any groups from the selection of controls in the design of the study but to analyze the study data separately for different diagnostic subgroups that constitute the control group.
What major concern can arise when conducting a case-control study?
A major concern when conducting a case-control study is the that cases and controls may differ in the characteristics or exposures other than the one that has been targeted for study.
Explain the process known as matching
Matching is defined as the process of selecting the controls so that they are similar to the cases in charatneriscs and can be of 2 types: individual matching and group matching.
Individual Matching- for each case that is selected for the study, a control is selected; who is similar to the cases in terms of specific variables of concern.
Group Matching (Frequency Matching)-consists of selecting the controls in such manner that the proportion of controls and cases with a certain characteristic is identical to each other.
What conceptual problems arise from matching during a case-control study?
1) Once we Match controls to a case according to a given characteristic we cannot study that characteristic; hence we do not want to match for many variable we wish to explore within our study.
2) It is also important to recognize that unplanned matching may occur within the study.
