POPH192 Lecture 19 - Cohort Studies

Question 1

what is analytic epidemiology?

Answer 1

examining associations with express and outcomes and thinking about causation
-can be undertaken by using observational or intervention study designs

Question 2

what is a cohort study?

Answer 2

observe peoples exposures and what happens to them

-individuals are defined on the basis on the basis of presence or absense of exposure to a suspected risk factor

Question 3

what are 6 the steps of a cohort study?

Answer 3

1) identify a source population
2) recruit your sample population (sample population must not already have the outcome of interest)
3) assess exposure to identify which group participants belong in (exposed or not exposed i.e comparison)
4) follow up over time
5) observe whether or not participants develop the outcome
6) calculate measures of occurrence and measures of association

Question 4

what can we measure using cohort studies?

Answer 4

measures of occurrence 
-incidence proportion (IP) 
-incidence rate (IR) 
measures of association
-relative risk
-risk difference (attributable risk)

Question 5

what is the equation for incidence proportion?

Answer 5

IP = number of people who develop the disease in a specific person / number of people at risk of developing the disease at the start of the period (always specify the time period)

Question 6

what is the equation for incidence rate?

Answer 6

IR= number of people who develop the disease in a specific period / number of person-years at risk of developing the disease (measure of the rate of disease onset)

Question 7

what are the two equations for relative risk?

Answer 7

1) rate ratio = IRe (incidence rate of the exposed group) / IRc (incidence rate of the comparison group)
2) risk ratio = IPe (incidence proportion of the exposed group) / IPc (incidence proportion of the comparison group)

Question 8

what are the 2 equations for risk difference?

Answer 8

1) IRe (incidence rate of the exposed group) - IRc (incidence rate of the comparison group)
2) IPe (incidence proportion of the exposed group) - IPc (incidence proportion of the comparison group)

Question 9

what is healthy worker effect?

Answer 9

when an occupational group is selected as the exposed group but the comparison group is selected from the general population

Question 10

what is the the result of the healthy worker effect?

Answer 10

people who are working are generally healthier than people who make up the general population
-form of selection bias

Question 11

what might we need to consider when following up over time?

Answer 11

• have participants changed exposure status over time?
• has everyone been followed up over the entire study? (lost to follow up)
• how long do participants need to be followed up? (depends on the study)

Question 12

what are the strengths of cohort studies?

Answer 12

• determine temporal sequence between exposure and outcome
• can examine multiple outcomes from an exposure
• can calculate incidence (and therefore relative risk and the risk difference)
• good for studying rare exposures (defining people based on exposure)

Question 13

what are the limitations of cohort studies?

Answer 13

• potential for misclassifications of exposures/outcomes
• generally not good for studying rare outcomes
• time consuming
• can be expensive

Question 14

what are the 2 types of cohort studies?

Answer 14

1) prospective cohort studies

2) historical cohort studies

Question 15

what are the 2 features of historical cohort studies?

Answer 15

1) use existing data

2) reconstruct follow-up period in the past because the outcomes have already occurred