Lecture 7, part 1

Question 1

Steps in cohort design

Answer 1

Population is divided into eligible and not eligible
Eligible pop is divided into exposed and unexposed
Exposed and unexposed are both divided into diseased and not diseased

Question 2

At the time the exposure status is determined in cohort studies, all potential subjects must be _________.

Answer 2

Disease-free

Question 3

What is the goal of cohort studies?

Answer 3

To compare the occurrence of the outcome (dz) across categories of the RFs or determinants (exposure)
To simulate the results of an experiment had one been possible

Question 4

How are cohort studies similar to experimental studies?

Answer 4

Make comparisons across two or more exposure groups
Follow participants to monitor for one or more outcomes
Groups selected to achieve comparability and efficiency
Relative proportion of subjects in compared groups might not reflect that of the general pop (generalizability issues)

Question 5

How are cohort studies different from experimental studies?

Answer 5

Participants are not randomized (no manipulation of exposure)
Participants generally self-select exposure and are aware of it

Question 6

What are the directions of cohort studies?

Answer 6

Prospective
Retrospective
Ambidirectional

Question 7

Aspects of prospective cohort studies

Answer 7

Outcomes have not occurred when study is initiated
Collect baseline (or ongoing) exposure information
Able to choose how to measure the outcome (and possibly the exposure)

Question 8

Aspects of retrospective cohort studies

Answer 8

Both exposures and outcomes of interest have already occurred when the study is initiated (only studies prior outcomes)
Useful for unusual exposures, occupational exposures, or dzs with long empiric induction periods
Relies on data collected by original researcher or clinician

Question 9

Aspects of ambidirectional cohort studies

Answer 9

Exposures and some outcomes have occurred when study is initiated, other outcomes have not yet

Question 10

For common RFs or exposures, from where should the sample be drawn?

Answer 10

General pop

Question 11

For rare exposures, from where should the sample be drawn?

Answer 11

Select “special cohorts” at higher risk

Question 12

What should occur for better data and compliance in terms of selecting a cohort pop?

Answer 12

Select a particular subset of the general pop
-Improved ability to obtain more complete and accurate info, easier to conduct f/u

Question 13

What are the two types of cohort pops?

Answer 13

Fixed
Dynamic

Question 14

Which are preferred- fixed or dynamic? Why?

Answer 14

Fixed because it is more difficult to establish eligibility and track ppl than in an open cohort (since they can enter/leave at any time)

Question 15

What are the ideal characteristics of the comparison group?

Answer 15

Would be exactly the same as the exposed group except that they would be unexposed
-Since this is impossible, comparison group should be as similar as possible to the exposed group on all other factors that might influence the outcome

Question 16

With the comparison group, what needs to be ascertained?

Answer 16

Baseline exposure(s) of interest as well as all possible confounding factors for both groups

Question 17

How can participants differ from non-participants?

Answer 17

May impact generalizability and validity of study results
Consider motivation for participation/retention in study
True exposure/outcome relationship will be biased if non-participation is related to both the exposure and/or other RFs for the outcome under study

Question 18

What are the types of comparison groups in cohort studies?

Answer 18

Internal comparison group
External comparison group
General population

Question 19

Strengths of internal comparison group

Answer 19

Most comparable to exposed group

Question 20

Weaknesses of internal comparison group

Answer 20

May be difficult to identify

Question 21

Strengths of external comparison group

Answer 21

Fairly comparable, might be easier to access/retain than sample from general pop

Question 22

Weaknesses of external comparison group

Answer 22

Results often difficult to interpret because comparison cohort often has other exposures

Question 23

Strengths of general population as comparison group

Answer 23

Accessible
Stable data

Question 24

Weaknesses of general pop as comparison group

Answer 24

Lack of comparability with exposed group
Healthy worker effect
Data on key variables may be missing

Question 25

What are good practices in measuring the exposure?

Answer 25

Should be as objective as possible (avoid bias)
Use previous methods if applicable
Can validate exposure measurement using a sub-sample or use multiple methods of measurement

Question 26

What should be done if exposure status is likely to change over time?

Answer 26

Repeated measurements