Cohort Studies

Question 1

T or F: Cohort studies have one of the strongest levels of evidence in observational studies.

Answer 1

True

Question 2

What is a cohort study?

Answer 2

Study that allows researcher to observe natural events in exposed and unexposed comparison groups.
Allocated based on EXPOSURE ignore disease status. OR group membership- brought together before study begins.

Question 3

What are cohort studies useful for?

Answer 3

Rare exposure, can generate risk of disease and RR

Question 4

In a two by two table what is known at the start of the study?

Answer 4

Rows ( A+B) and (C+D) who has been exposed

Question 5

What are reasons to use a cohort study?

Answer 5

Unethical to force allocation
Limited time money and subjects- more $$ and time than case control but less than interventional
Exposure is rare little known about outcomes
More interested in incidence rates for outcome (prospective)

Question 6

How can a cohort study be conducted?

Answer 6

Prospectively
Retrospectively
Ambidirectional

Question 7

How is a prospective study set up?

Answer 7

Still choose groups based on membership or exposure status. Exposure is selected based on past or current exposure and followed into future to see what occurs. Outcomes not known.

Question 8

How is a retrospective study set up?

Answer 8

At the start of the study both exposure and disease status is known, but groups are still chosen based on past history of exposure. Start at time of exposure historically and travel to present time.

Question 9

Ambidirectional study set up?

Answer 9

Uses retrospective data to assesss past differences up to the present and then adds future data.

Question 10

What is a birth cohort?

Answer 10

Those born in a geographic region at a given time period

Question 11

Inception cohort?

Answer 11

Something in common at a given period of time- where people live or work useful for single group assessments for incidence
Nurses Health Study or Framingham Study can come and go

Question 12

Exposure cohort?

Answer 12

Individuals assemble based on one common exposure usually one time event. Can’t be added to group
Ex: 9/11 first responders

Question 13

What is a fixed cohort?

Answer 13

Derived from irreversible event cant gain members but can have LTF. WW2 veterans, 9/11 first responders, Holocaust survivors

Question 14

Closed Cohort?

Answer 14

Short enough duration there is no LTF

Question 15

Open or Dynamic Cohort?

Answer 15

Come and go overtime- nurses health study

Question 16

How to select exposed study population?

Answer 16

Allocate subjects based on pre defined criteria for exposure.

Question 17

How to select unexposed study population?

Answer 17

Make the groups as close as possible can come from:

1. Internal: within the cohort who are not exposed
2. Population: when cohort is not usable.
3. Comparison Cohort: Least acceptable match groups as close as possible on personal characteristics cant control for other exposures though.

Question 18

General strengths of cohort studies?

Answer 18

Can assess multiple outcomes from one exposure
Rare exposures
Calculate RR(Prospective)
Good when ethics limits
Good for long induction period (retrospective)
Represent temporality (prospective)

Question 19

General Weaknesses of Cohort studies?

Answer 19

Cant demonstrate causation
Hard to control for multiple exposures (esp. retro)
Can be impacted by unassessed confounders (Retro)
Impacted by biases-select, recall,assess (Retro)
Limited by data (Retro)

Question 20

Advantages of prospective studies?

Answer 20

Can obtain more detailed information
Can follow up track patients easier
Better at temporality
Calculate risk and incidence rates

Question 21

Disadvantages to prospective studies?

Answer 21

Not good for long induction latent period diseases
Not good for rare diseases
A lot of time and high LTF

Question 22

Problems with LTF in prospective studies?

Answer 22

Decreases power, increases risk of type 2 error

Question 23

Advantages to retrospecitve?

Answer 23

Good for long induction latenet periods
Rare exposures
Useful if data exists
Save time and money compared to prospective

Question 24

Disadvantages to retrospective?

Answer 24

Have to have access to charts and databases and records could be incomplete or lacking.
Patients may not be available
Exposure or amount could have changed over time

Question 25

Key Biases in Cohort Studies?

Answer 25

Healthy worker bias and Selection bias