Cohort Studies

Question 1

What are three ways that a cohort study can be conducted?

Answer 1

The cohort study can be conducted based on time. -prospective -retrospective -ambidirectional

Question 2

What is an ambidirectional cohort study?

Answer 2

An ambidirectional cohort study uses retrospective and prospective information. -looking for outcomes in the past and into the future.

Question 3

What is a retrospective cohort study?

Answer 3

A retrospective cohort study is a study that uses records of historical exposure and the presence of outcome.

Question 4

What is a prospective cohort study?

Answer 4

A prospective cohort study is designed to study an exposed group of a past or current exposure and followed into the future for a potential outcome.

Question 5

What is the definition of cohort?

Answer 5

Cohort is a group of people with something in common.

Question 6

What is inception cohort?

Answer 6

Group of individuals assembled at a given point based on some common factor

example:

• where people work/live
• delivering mothers and what instrument was used at time of their labor
• Framingham, MA

Question 7

What is a fixed cohort?

Answer 7

A fixed cohort is a group derived from an irrevocable event which can’t gain members but can have loss-to-follow ups. example: those experience 9/11

Question 8

What is a closed cohort?

Answer 8

A closed cohort is a group that cannot add new members or have any loss-to-follow-ups

Question 9

What is an open cohort?

Answer 9

An open cohort is a cohort with new additions and some loss-to-follow-ups over time.

Question 10

How are subjects allocated in the cohort study design?

Answer 10

Subjects are allocated in groups within the cohort study design by exposure.

Question 11

What type of study design is a cohort study? a) interventional b) observational

Answer 11

b) Cohort studies are observational and analytical. They have the most strength in evidence of all observational studies.

Question 12

In cohort studies, how are groups allocated?

Answer 12

Groups are allocated based on exposure-status or group status

Question 13

What are the advantages of a cohort study design?

Answer 13

-useful in an unethical exposure (groups were naturally exposed) - requires little resources (time, money, subjects) -useful when the exposure is rare -useful when interested in rates/predictors of risks for outcome of interest.

Question 14

What is the common measure of association in cohort studies?

Answer 14

Cohort studies commonly generates risk ratio (RR) as measure of association.

Question 15

What is birth cohort?

Answer 15

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

Question 16

What is exposure cohort?

Answer 16

Exposure cohort is a group of individuals assembled based on some common exposure

Example: Firefighters exposed to 9/11 disaster

Question 17

What are 3 sources we can get our unexposed group from?

Answer 17

1) internal
2) general population
3) comparison cohort

Question 18

What is an internal source from which one can collect an unexposed group?

Answer 18

Patients from the same “cohort”, yet who are unexposed (most similar).

This is the best, if feasible.

Question 19

What does it mean to select your unexposed group from the general population?

Answer 19

Just selecting the unexposed groups from the general population.

Question 20

What does it mean to select your unexposed study population from a comparison cohort?

Answer 20

Attempt to match groups as close as possible on numerous personal characteristics.

This is the least acceptable group.

Question 21

what are the strengths of cohort studies?

Answer 21

1. good for assessing multiple outcomes of one exposure
2. useful when exposure is rare
3. useful in calculating risk and RR’s
4. less expensive
5. useful when ethical issues limit use of interventional
6. good for long induction/latent periods (retro)
7. able to represent “temporality” (prospective)

Question 22

Which study allows you to obtain a greater amount of study-important information from patients? retro or prospective?

Answer 22

Prospective because researchers have more control over specific data collection process.

Question 23

What are advantages of a prospective study?

Answer 23

• more info
• patient follow-up easier
• gives answers to “temporality”
• look at multiple outcomes form a single exposure
• calculate incidence and incidence rates

Question 24

What are the disadvantages of a prospective study?

Answer 24

• time, expense, and lost-to-follow-up’s
• not efficient for rare diseases
• not suited for long induction/latency conditions
• exposure may change over time

Question 25

What is the concern over loss-to-follow-ups in prospective cohort studies?

Answer 25

• lowers sample size and therefore power
• increased risk of type II error
• study participation may become unequal between groups

Question 26

True or False. Authors do not have to report loss-to-follow-ups by group.

Answer 26

False. Author’s MUST list loss-to-follow-ups by group (exposed/unexposed).

Question 27

What are the advantages of retrospective cohort studies?

Answer 27

• useful for long induction/latency conditions
• study rare exposures
• useful if data already exists
• saves time and money

Question 28

What are the disadvantages of restrospective cohort studies?

Answer 28

• requires access to records (may be sensitive)
• info may not factor in or control for other exposures to harmful elements
• patients not available for interview
• exposure may have changed over time.

Question 29

What 3 issues affecting outcome occurrence in groups?

Answer 29

1. level of exposure
2. induction period
3. latency period

Question 30

What are 2 biases to be cautious of in cohort studies?

Answer 30

1. healthy-worker effect
2. selection bias

Question 31

What is the healthy work effect bias?

Answer 31

if you use employed people as test population you won’t include people too sick to work. As a result you select a decently healthy group of people.

Question 32

What is the selection bias?

Answer 32

How exposure status is defined/determined (less of an issue with exposure status)