Cohort studies (Lecture 4) Flashcards Preview

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Define a cohort study

observational studies that allow a researcher to be a passive observer of natural events occurring in a naturally exposed and unexposed groups


What is the group allocation of the cohort studies based on?

1. exposure status
2. group membership


When are cohort studies useful?

When studying a rare exposure


What are two other names for a cohort study?

Incidence studies and longitudinal studies


What two measures of association are typically used in a cohort study?

risk of the disease or the outcome and the risk ratio or the relative risk


What are the reasons to pick a cohort study?

-unable to randomize or force the group allocation
-limited resources
-exposure of interest is rare
-more interested in the incidence or risk rates


What are the 3 ways in which a cohort study can be conducted in?



Define a prospective cohort study

exposure group is selected on the bases of past or current exposure and both groups are following into the future to assess for the outcomes


Define a Retrospective cohort study

At the start of the study, the exposure and the source has already occurred bit the groups are still allocated based on the past history of the exposure


What is another word for a retrospective study?



Where do you start at in a retrospective study?

At the time of exposure (historically- it is in the past) and then you follow it forward to the point of outcome that is in the present

*exposure has to occur before the outcome of interest and the group allocation is based on exposure status, not the disease status


Define an ambidirectional cohort study

Uses retrospective design to assess past differences but also adds future data collected on additional outcomes prospectively from the start of the study


How is an ambidirectional study considered to be bidirectional?

Looking for outcomes that are in the past and that are known in the present but also looks into the future


Define cohort

reders to a group with something in common


Define birth cohort

individuals that are grouped together based on being born in a geographic region in a given time period


Define inception cohort

Individuals that are grouped together at a given point based on a common factor
-where people live, where they work, something they have in common


Define exposure cohort

Individuals are assembled together based on a common exposure


True or false
Cohort changes cannot change over time

False: they may or may not change over time


Define a fixed cohort

a cohort which cannot gain members but can have loss to follow ups


Define a closed cohort

A fixed cohort with no loss to f/u


Define an open (dynamic) cohort

A cohort with new additions and some loss to f/u


How do you select the exposed study populations?

You allocate the subjects based on a predefined criteria of exposure


What are the goals of an unexposed study population?

To make the groups as close as possible (coming from the same cohort while also being unexposed)


What are the 3 sources that an unexposed group can come from?

1. Internal
2. General population
3. Comparison cohort


Describe the internal source of unexposed selection

patients come from the same "cohort" but are unexposed
If there are levels of exposure, use the lease exposed group as a comparator



Describe the general population selection group for the unexposed study population

used if the internal source is not available
everyone is exposed; the exposure subjects came from the general population


Describe the comparison cohort source of an unexposed selection

This is the LEAST acceptable
attempts to match the groups as close as possible on personal characteristics

cannot control for the other potentially harmful exposures in the comparison cohort


What are the strengths of a cohort study?

1. Multiple outcomes
2. rare exposures
3. calculating risk and RR
4. ethical issues are limiting the interventional, can use cohort
5. long conduction/latent periods (retro)
6. "temporality" (prospective)


What are the weaknesses of a cohort study?

1. Cannot demonstrate causation
2. hard to control for other exposures if more than one plausible for being associated with an outcome
3. retrospective cannot control for other exposures or potential changes in amount of study exposure
4. not good for long induction /latent period (prospective; retrospective is better)
5. impacted by unassisted confounders
6. impacted by biases (selection and recall)
7. limited by available data (retrospective; less for prospective)


What are the advantages of a Prospective cohort study?

1. can obtain a greater greater amount of info from patients
-more control over specific data collection
2. Follow up may be easier
3. Temporality
4. Multiple outcomes for a single exposure
5. Can calculate incidence and incidence rates

Inclusive- info
Friends- Follow up
Talk to- temporality