Cohort Studies

Question 1

relate cohort studies to strength in evidence of all observational studies

Answer 1

has the most evidence

only observational that can be a controlled prospective study

Question 2

cohort studies are _______ studies that allow the researcher to be …..

Answer 2

observational

a passive observer of natural events occurring in naturally exposed or unexposed groups

Question 3

group allocation is based upon?

Answer 3

exposure status
or
group membership—simply something in common

Question 4

cohort studies are useful when studying ?

Answer 4

a rare exposure

Question 5

other terms for cohort studies

Answer 5

incidence studies

longitudinal studies

Question 6

what measures of association do cohort studies calculate?

Answer 6

1. risk of disease/outcome

2. RR/relative risk

Question 7

define cohort

Answer 7

a group of people who simply have something in common

and then you can further allocate them into groups based upon exposure or not/ or disease/ not diseased

Question 8

reasons to choose a cohort design

Answer 8

1. unable to randomize
2. limited resources
3. exposure of interest is rare
4. more interested in incidence rate or risk of outcome than an intervention

Question 9

exposure of interest is rare

Answer 9

• -rarely occurs

- -little is known about its associations or outcomes

Question 10

time line direction of cohort studies

Answer 10

can be prospective, retrospective, or ambidirectional fashion

Question 11

prospective cohort studies

Answer 11

1. exposure groups is selected based on past or present exposure
2. both groups are followed into future to assess for outcomes

Question 12

historical cohort study = ?

Answer 12

retrospective design

Question 13

retrospective cohort studies

Answer 13

1. at start of study exposure and outcome has already occurred
2. but groups are still allocated based on past history of exposure
3. not disease status

Question 14

ambidirectional design

Answer 14

• -uses past exposure for group allocation
• -adds present data and
• –keeps going in a prospective fashion

Question 15

birth cohort

Answer 15

–individuals assembled into a cohort based upon being born in same region/in same time period

Question 16

inception cohort

Answer 16

–individuals assembled in a cohort at a specific time based upon a common factor

–ex. cob class– all in this grad program

Question 17

exposure cohort

Answer 17

• -brought together based upon some common exposure

ex. 9/11 responders – exposed to carcinogens

Question 18

cohort sizes may ______ over time

Answer 18

not change

Question 19

cohort size control

Answer 19

1. fixed cohort
2. closed cohort
3. open/dynamic cohort

Question 20

fixed cohort

Answer 20

a cohort which cannot gain members but can have lost to follow-up

Question 21

closed cohort

Answer 21

a fixed cohort but no loss to follow-up

Question 22

open cohort

Answer 22

• -dynamic cohort
• –a cohort w/ new additions and some loss to follow-up
• ex. nurse health

moving, death, etc.

Question 23

sources of the unexposed group

Answer 23

1. internal
2. general population
3. comparison cohort

Question 24

internal source

Answer 24

1. best option
2. patients from same cohort yet unexposed
3. use lowest exposure group when levels of exposure exist

Question 25

describe levels of exposure

Answer 25

--when exposure intensity increases/decreases over time - -in some events there are no unexposed subjects - -comparison group may just have to be the lowest exposure people

Question 26

general population

Answer 26

1. a second choice when an internal group is not available

Question 27

comparison cohort

Answer 27

1. the least favorable group | 2. simply match groups as close as possible on personal characteristics

Question 28

strengths of cohort design

Answer 28

1. good for multiple outcomes of one exposure 2. rare exposures 3. calculate risk and RR 4. less expensive 5. less ethical limits 6. good for retrospective 7. can be prospective

Question 29

matching in cohort studies

Answer 29

--a way to strive to make groups as equal as possible for known confounders

Question 30

key biases in cohort studies

Answer 30

healthy worker effect selection bias

Question 31

weaknesses of cohort studies

Answer 31

1. can't show causality 2. can't control variables in retro 3. retro can't control for other exposures 4. prospec not good for long induction periods 5. impacted by unknown confounders 6. effected by biases 7. limited by available data when retro

Question 32

advantages of prospective cohort studies

Answer 32

1. obtain greater amount of specific data 2. tracking subjects easier 3. can assess temporality 4. can eval multiple outcomes of one exposure 5. calc incidence risk and rate

Question 33

disadvantages of prospective cohort studies

Answer 33

1. time, money, lost to follow up 2. not great for rare diseases 3. not suited for long induction or latent periods 4. exposure can change -- levels of exposure

Question 34

lost to follow up in prospective designs

Answer 34

- -a problem just like in interventional designs | - -increases risk of type 2 error

Question 35

advantages of retrospective cohort designs

Answer 35

1. best for long induction/latent periods 2. study rare exposures 3. useful when data already exists 4. saves time and money compared to prospec

Question 36

disadvantages of retrospective cohort designs

Answer 36

1. requires access to data 2. cannot control for variables or other exposures 3. patients might not be available for contact 4. exposure can change over time -- levels