Cohort studies

Question 1

Cohort studies definition

Answer 1

Observational studies allowing researcher to be a passive observer of natural events occurring in naturally exposed and unexposed comparison groups

Question 2

Group-allocation based on

Answer 2

Exposure status or
Group membership (something in common), not group allocation based

Question 3

Useful when

Answer 3

Studying a rare exposure

Question 4

Other names for cohort studies

Answer 4

Incidence studies/longitudinal studies

Question 5

Reasons to select cohort studies

Answer 5

Unable to force group allocation
Limited resources
Exposure of interest is rare
More interested in incidence rates or risks for outcome of interest

Question 6

Cohort studies can be conducted in which fashions

Answer 6

Prospective, retrospective, or ambidirectional fashion

Question 7

Prospective cohort studies

Answer 7

Exposure group is selected on the basis of a past or current exposure and both groups followed into future to assess for outcomes of interest (which has yet to occur)

Question 8

Retrospective cohort studies

Answer 8

At the start of the study, both exposure and outcome of interest have already occurred, but groups still allocated based on past history of exposure
Exposure still must occur before outcome

Question 9

Ambidirectional cohort studies

Answer 9

Uses retrospective design to assess past difference, but also adds future data collected on additional outcomes prospectively from start of study
–Looking for outcomes in the past, and known in the present, but also in the future

Question 10

Cohort also refers to

Answer 10

A group with something in common

Question 11

Birth cohort

Answer 11

Individuals assembled based on being born in a geographic region in a given time period

Question 12

Inception cohort

Answer 12

Individuals assembled at a given point based on some common factor

• where they live/work
• useful for single group assessments for incidence rate determination

Question 13

Exposure cohort

Answer 13

Individuals assembled based on some common exposure

Question 14

Fixed cohort

Answer 14

A cohort which cant gain members but can have loss to follow ups

Question 15

Closed cohort

Answer 15

A fixed cohort with no loss to follow ups

Question 16

Open/dynamic cohort

Answer 16

A cohort with new additions and some lost to follow ups

Question 17

Unexposed group can come from what three sources

Answer 17

Internal (best source)
General population (2nd choice)
Comparison cohort (least accepted)

Question 18

Strengths of retrospective cohort studies

Answer 18

Best for long induction/latency periods
Able to study rare conditions
Useful if the data already exists
Saves time and money compared to prospective

Question 19

Weaknesses of retrospective cohort studies

Answer 19

Cant demonstrate causation
Hard to control for other exposures
Must have access to old records
Can be impacted by unassessed confounders and various biases (selection/recall/assessment bias)
May not be able to interview study subjects

Question 20

Weakness of prospective cohort

Answer 20

Not good for long induction/latent periods
Time, expense, lost to follow up
Not efficient for rare diseases
Exposure may change over time

Question 21

Strengths of prospective cohort studies

Answer 21

Can obtain larger amount of study-important info from patients
Follow-up/tracking of patients easier
Better at giving answer to temporality
May look at multiple outcomes from single exposure
Calculate incidence and incidence rates

Question 22

Key biases with cohort studies

Answer 22

Healthy-worker bias

Selection bias