Cohort Studies

Question 1

What are cohort studies?

Answer 1

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

Question 2

In cohort studies, what is group allocation based on?

Answer 2

exposure status or group membership (something in common)

Question 3

When are cohort studies useful?

Answer 3

when studying a rare exposure

Question 4

What are the reasons to select a cohort design?

Answer 4

unable to force group allocation
limited resources
exposure of interest is rare
more interested in incidence rates or risks for outcome of interest

Question 5

What ways can cohort studies be conducted?

Answer 5

prospective, retrospective, ambidirectional

Question 6

What is a prospective cohort study?

Answer 6

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, then compared

Question 7

What is a retrospective cohort study?

Answer 7

at the state of the study both exposure and outcome of interest of already occurred, but groups still allocated based on past history of exposure

Question 8

What is an ambidirectional cohort study?

Answer 8

uses retrospective design to assess past differences (up to present), but also adds future data collected on additional outcomes prospectively from start of study

Question 9

What is a cohort?

Answer 9

group with something in common

Question 10

What is a birth cohort?

Answer 10

individuals assembled based on being born in a geographic region in a give time period

Question 11

What is an inception cohort?

Answer 11

individuals assembled at give point based on some common factor

Question 12

What is an exposure cohort?

Answer 12

individuals assembled based on some common exposure

Question 13

What is a fixed cohort?

Answer 13

cohort which can’t gain members but can have loss to follow ups

Question 14

What is a closed cohort?

Answer 14

a fixed cohort with no loss to follow ups

Question 15

What is an open or dynamic cohort?

Answer 15

a cohort with new additions and some loss to follow ups

Question 16

How do you select an exposed study population in cohort studies?

Answer 16

allocate subjects based on pre defined criteria of exposure

Question 17

How do you select unexposed study population in cohort studies?

Answer 17

make groups as close as possible (coming from same cohort/population, yet not exposed)

Question 18

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

Answer 18

internal
general population
comparison cohort

Question 19

What is an internal source?

Answer 19

patients from the same cohort, yet are unexposed

Question 20

What is the general population source?

Answer 20

used as second choice, unexposed subjects drawn from general population

Question 21

What is a comparison cohort source?

Answer 21

least acceptable group
simply attempt to match groups as close as possible on numbers personal characteristics (can’t control for other potentially harmful exposures in comparison cohort, also causing disease)

Question 22

What are the strengths to cohort studies?

Answer 22

• good at assessing multiple outcomes of one exposure
• useful when exposures are rare
• useful in calculating risk and risk ratios
• less expensive
• good when ethical issues limit interventional
• good for long induction/latent periods (retrospective)
• able to represent temporality

Question 23

What are the weaknesses of cohort studies?

Answer 23

• can’t demonstrate causation
• hard to control for other exposures if more than one plausible for being associated with an outcome
• retrospective can’t control for other exposures or potential changes
• not good for long induction/ latent periods (prospective)
• can be impacted by unassessed confounders
• can be impacted by various biases
• limited by available data

Question 24

What are the advantages to prospective cohort studies?

Answer 24

• can obtain a greater amount of study important information from patients
• follow up/ tracking of patients may be easier
• better at giving answer to temporality
• may look at multiple outcomes form a single exposure
• can calculate incidence and incidence rate

Question 25

What are the disadvantages to prospective cohort studies?

Answer 25

• time, expense, and lost to follow up
• not efficient for rare diseases
• not suited for long induction/ latency conditions
• exposure (or its amount) may change over time

Question 26

When it comes to loss to follow up, do all you can to ____

Answer 26

limit them

Question 27

What are the advantages to retrospective cohort studies?

Answer 27

• best for long induction/latency conditions
• able to study rare exposures
• useful if the data already exists
• saves time and money compared to prospective

Question 28

What are the disadvantages to retrospective cohort studies?

Answer 28

• require access to charts, databases, employment records, etc.
• information may not factor in or control for other exposures to harmful elements during study period or over time
• patients may not be available for interview if contact necessary for missing or incomplete data
• exposure may have changed over time

Question 29

What are the key biases in cohort studies?

Answer 29

health worker effect

selection bias