Ch. 9 Cohort Studies Flashcards
Refresher: What is the Most important 2 features that must be consistent in the study design of any epidemiological study?
1) We determine if there is an association between a factor or a characteristic of a factor and the development of a disease. Which can ultimately be done by studying the characteristics of groups, individuals, or both.
2) We derive appropriate inferences regarding a possible casual relationship from the patterns of association that have been found.
Explain the Design of a Cohort Study.
In a cohort study, the investigator selects 2 or more groups of exposed and non-exposed individuals and follows them for an extended period of time (time may vary but can be years later) to compare the rate of incidence or deaths from a disease between the groups.
True or False: In a positive association we would see all of the groups develop the disease and thus an increase in the incidence would occur.
False. In a positive association we would see an increase portion of the exposure group develop the disease and thus an increase in the incidence would occur in the exposed group.
How do you calculate incidence? Ex - 2 groups
a/a+b
True or False: Thus the purpose of a cohort study is because we are identifying new induce rates cases of disease as they occur, we determine whether or not a temporal relationship exists where the disease develops after exposure.
True.
What is the key difference between a cohort study and a Randomized trial?
The presence or absence of randomization.
When we observe an association of an nonrandomized study what are some of the uncertainties between of an exposure to a disease are we likely to see?
The uncertainty can lead to the misinterpretation of the results, where the factors which led to the people to exposure that are associated with the disease rather than the people not being randomized to the exposure
When selecting a group to participate in a cohort study what 2 designs can be used in the selection process?
1) Selecting a the group populations for inclusion of the study on the basis of whether or they have been exposed.
2) Select a defined population before any of its members have been exposed or have been identified by recording the populations history through various testing.
What is a ProspectiveConcurrent Cohort Study?
Concurrent Cohort Study is one in which the investigator identifies the original population ad accompanies then through calendar time as the disease develops.
Define Retrospective Cohort study.
Retrospective Cohort Study uses the same design as a the cohort but in addition to the use of historical data gathered.
What potential Biases can occur in a cohort study?
1) Bias in the assessment of the outcome due to previous knowledge of the exposure.
2) Information Bias in regard to the amount of information or quality of information gathered from the exposed and non-exposed groups.
3) Bias due to non-response and loss to follow-up
4) Analytic Bias epidemiologist may introduce their own bias.
When is a cohort study warranted?
When good evidence suggest a possible association of disease with a certain exposure obtained through clinical observation, case-control, or other forms of scientific field study.
