Module 10 Flashcards
Prospective Cohort Study
A research study that 1. starts with a group of exposed and unexposed individuals 2. Who are free of a health outcome of interest at the start of the study and who 3. are followed over time to assess the development of a health outcome.
A prospective cohort study is concurrent because the investigator identifies the original population at the beginning of the study and, in effect, follows the subjects concurrently through calendar time until the point at which the disease develops or does not develop.
Retrospective cohort study
A research study in which information on the exposures of interest have already been collected in the past (historically) at the start of the study, for example through historical medical records
The study design of a retrospective cohort study does not differ from that of a prospective study - we are still comparing exposed and unexposed groups
Which guideline for assessing causality can be determined using a cohort study design?
Temporality, since individuals are free of the disease at the beginning of the study. This is a major advantage of cohort study.
What is the difference between a prospective and retrospective cohort study?
The only difference between a prospective and retrospective cohort study is calendar time. In a prospective cohort design, exposure status is ascertained at the beginning of the study, and these groups are followed into the future. In a retrospective cohort design, the exposure status is obtained from past records, and the disease status is determined when the study begins.
What measures of association can be calculated in a cohort study?
CIR, IRR, and OR can all be calculated
Are cohort studies good for rare exposure or rare outcomes?
Cohort studies are good for rare exposures because researchers can make sure to include enough people with the exposure when recruiting the sample, but they are not good for rare outcomes because they would need hundreds of thousands of participants to ensure that enough participants developed the health outcome to have an adequate sample size
What is the main advantage of cohort studies?
The temporal order of associations between the exposure and outcome can be determined
What is the main source of selection bias in cohort studies?
Differential loss to follow-up (e.g., loss to follow-up is associated with the exposure and outcome, or variables associated with the exposures and outcome.)
What are the two steps to determining disease etiology?
- determine if there is an association
- derive appropriate causal inferences to determine if there is a causal relationship
What are the two basic ways of creating a study population for a cohort study?
- We can create a study population by selecting groups based on their exposure
- We can select a defined population before any exposure takes place (will require a longer time for follow up)
What are the types of selection bias found in a cohort study
nonparticipation and nonresponsiveness
- who joins a study
- who is lost to follow-up
What are the types of information bias typical of a cohort study
data gathering: quality and extent of the information may be different for exposed and unexposed
Researcher bias
Analysis bias
What are the advantages of a prospective cohort study
- We can understand the temporal order of associations
- We can assess the incidence/risk of a health outcome
- We can apply them to rare exposures because we can recruit people
- We can assess the effects of exposure on multiple health outcomes
- There is a lower risk of selection and recall bias
What are the disadvantages of a prospective cohort study
- They take a long time to conduct
- They are expensive
- They are not good for rare outcomes
- Loss to follow up can result in selection bias
What are the advantages of a retrospective cohort study?
- We can understand the temporal order of associations
- We can assess the incidence/risk of a health outcome
- We can apply them to rare exposures because we can recruit people
- We can assess the effects of exposure on multiple health outcomes
- They take less time than prospective studies
What are the disadvantages of a retrospective cohort study?
- They are not good for rare outcomes or outcomes with long latency periods
- They often use data that is not designed for the purpose of the study
- They can have the potential for differential loss to follow up
- Because participants may have the health outcome in the calendar time that the study starts, there is a risk for selection bias when sampling the cohort and information bias in assessing the exposure and health outcome
