Lecture 19

Question 1

how are individuals defined in a cohort study

Answer 1

on the basis of presence or absence of exposure to a suspected risk factor

Question 2

how do cohort studies work

Answer 2

1. sample population recruited (they must not already have the outcome)
2. assess exposure to identify which group participants belong to (exposed or comparison)
3. follow up over time
4. calculate measure of occurrence and measures of association

Question 3

what measures of occurrence can be measured from a cohort study

Answer 3

incidence proportion and incidence rate

Question 4

what measures of association can be measured from a cohort study

Answer 4

• relative risk
• risk difference or attributable risk

Question 5

when selecting people to be in a cohort study what should we focus on doing (ideal and sometimes)

Answer 5

ideal : random selection independent of exposure status

sometimes : selection based on exposure status, must consider appropriate comparison group

Question 6

what are the strengths to a cohort study ?

Answer 6

• can determine temporal sequence between exposure and outcome
• can study lots of different outcomes that may be related to a single exposure
• calculate incidence (therefore relative risk and risk difference)
• good for studying rare exposures

Question 7

what are the limitations to a cohort study ?

Answer 7

• loss to follow up
• potential for misclassification of exposure / outcome
• generally not good for rare outcomes
• time consuming
• can be expensive

Question 8

what is a historical cohort study

Answer 8

use existing data that has been collected for a different purpose

Question 9

strengths of a historical cohort study

Answer 9

• less time consuming compared with prospective cohort studies
• good for outcomes that takes a long time to develop
• less expensive

Question 10

limitations of historical cohort studies

Answer 10

• uses existing data = unsure about the quality
• may not know all relevant factors

Question 11

what is the difference between prospective and historical cohort studies

Answer 11

• prospective cohort studies identify people and then group them based on if they have the exposure or not, then follow them to see if they develop the outcome
• historical cohort studies use existing of people being exposed and see if they have the outcome