22-23 Cohort Studies

Question 1

How are cohort studies setup?

Answer 1

based on exposure, looking for outcome

Question 2

Define cohort studies.

Answer 2

observational analytical studies allowing researchers to be passive observers of natural events occurring in naturally-exposed and unexposed (comparison) groups

Question 3

What are cohort studies also termed?

Answer 3

incidence studies, follow-up studies, longitudinal studies

Question 4

When are cohort studies useful?

Answer 4

when studying a rare exposure

Question 5

What does cohort studies commonly generate?

Answer 5

risk ratios as a measure of association

Question 6

Can cohort studies be conducted in a prospective, retrospective, or ambidirectional fashion?

Answer 6

yes

Question 7

List the reasons not to chose a cohort study

Answer 7

Unable to randomize

limited resources

the exposure of interest is rare in occurrence and little is known about its associations/causes

more interested in incidence rates/predictors of or risks for outcome of interest

Question 8

Describe a prospective cohort study.

Answer 8

exposure group is selected on the basis of a past or current exposure and both groups followed into the future to assess for outcomes of interest and then compared

Question 9

Describe a retrospective cohort study.

Answer 9

at the start of the study, both the exposure and the outcome of interest have occurred
- retrospectively start at time of exposure and follow forward to the point of outcome occurrence in the present

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

Question 10

Describe an ambidirectional cohort study.

Answer 10

uses retrospective design to assess past differences but adds all data collected on additional outcomes prospectively from start of study
- looking for outcomes in the past and into the future

Question 11

What does a cohort study refer to?

Answer 11

a group with something in common

Question 12

Give examples of cohort studies.

Answer 12

Birth cohort

Inception cohort

exposure cohort

Question 13

Describe birth cohort.

Answer 13

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

Question 14

Describe inception cohort.

Answer 14

individuals assembled at a given point based on some common factor
- where people live, work, etc.

Question 15

When is inception cohort studies useful?

Answer 15

for single-group non-comparisons for incidence rate determination

Question 16

Describe an exposure cohort study.

Answer 16

Individuals assembled based on some exposure

- frequency connected to environmental or other one-time events

Question 17

Give the different types of cohort studies.

Answer 17

Fixed: can’t gain members but can have loss to follow ups

Closed: fixed with no loss to follow ups

open: new additions and some loss to follow ups; can increase or decrease over time

Question 18

How would you select an exposed study population?

Answer 18

allocate subject based on pre-defined criteria of exposure

Question 19

How would you select an unexposed study population?

Answer 19

make the groups as close as possible

unexposed group can come from 3 sources
- internal population, general population, comparison cohort

Question 20

Describe internal population.

Answer 20

Patients are from the same “cohort” yet who are unexposed

if there are only levels of exposure you have to use the lowest exposure group as comparator

Question 21

When would you use a general population?

Answer 21

when everyone is exposed, or the exposure subjects were drawn from the general population

Question 22

What does a comparison cohort attempt to do?

Answer 22

match groups as close as possible on numerous personal characteristics

Question 23

Can a comparison cohort study control for other potentially harmful exposures in comparison?

Answer 23

No

Question 24

List the strengths of cohort studies.

Answer 24

Good for assessing multiple outcomes of one exposure

useful when exposures are rare

useful in calculating risk and RR’s

less expensive than interventional trials

good when ethical issues limit use of interventional studies

good for long induction/latent periods (retrospective)

able to represent “temporality” (prospective)

Question 25

What are the advantages of prospective cohort studies?

Answer 25

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 from a single exposure

can calculate incidence & incidence rates

Question 26

What are the disadvantages of prospective cohort studies?

Answer 26

time, expense, & lost to follow up’s

not efficient for rare diseases

not suited for long induction/latency conditions

exposure may change over time

Question 27

What is the effect of loss to follow ups?

Answer 27

lowers sample size

increase risk of type 2 error

study population may not be equal between groups

Question 28

What are the advantages of retrospective cohort studies?

Answer 28

best for long induction/latency conditions

able to study rare exposures

useful if the data already exists

saves time and money compared to prospective cohort studies

Question 29

What are the disadvantages of retrospective cohort studies?

Answer 29

requires access to charts, databases, employment records

information may not factor in or control for other exposures to harmful elements

patients may not be available for interview if contact necessary for missing or incomplete data

exposure may have changed over time

Question 30

What are the issues affecting outcome occurrence in groups?

Answer 30

level of exposure: stratify

Induction Period

Latency period

Question 31

Define induction period.

Answer 31

interval between exposure which causes disease and onset of disease-process

Question 32

Define latency period.

Answer 32

interval between disease-process onset & clinical diagnosis of disease

Question 33

What is one way researcher strive to make the groups as equal as possible on known/potential confounders in cohort studies?

Answer 33

matching

Question 34

List and describe the key biases with cohort studies.

Answer 34

Healthy-worker effect
- if healthy, you work (even if exposed). if too ill to work (due to exposure?)you may be unemployed (now part of non-working general population).

Selection bias
- how exposure status is defined/determined (less of an issue with exposure status)

Question 35

Of all the study designs, which one is the only one that touch at the concept of temporality?

Answer 35

cohort studies

Question 36

Give an example of a fixed cohort study.

Answer 36

first responders of 9/11

Question 37

Give an example of a closed cohort study.

Answer 37

short term studies

Question 38

Give an example of an open cohort study.

Answer 38

Framingham Heart Study