Cohort Study

Question 1

Process of conducting study

Answer 1

1) Research question – takes form is exposure associated with outcome
2) Identify study population – based on how common exposure is, if common separate at start, if rare we choose population known to be exposed then a comparison group
3) Measure exposure – define exposure, how has been ascertained and how often been measured. Also measure likely confounding variables
4) Follow up participants and determine outcome – define outcome, how is ascertained, do all populations have similar risk of outcome, has population at risk changed over time
5) Data analysis – results as risk or rate (frequency of outcome in exposed group compared to not exposed group), then risk or rate ratio
6) Interpret results – RR>1 means risk in exposed greater than not exposed (positive association, need to determine if causal)
7) Assess sources of error – bias, confounding factors

Question 2

What calculation is performed in cohort studies

Answer 2

Risk ratio

Question 3

Risk ratio formula

Answer 3

Risk ratio = risk exposed / risk not exposed

Question 4

Risk difference formula

Answer 4

Risk difference = risk exposed - risk not exposed

Question 5

Rate ratio formula

Answer 5

Rate ratio = rate exposed / rate not exposed

Question 6

Rate difference formula

Answer 6

Rate difference = rate exposed - rate not exposed

Question 7

When is risk ratio and rate ratio used

Answer 7

Risk ratio - working with total number people
Rate ratio - working with person time

Question 8

What is person time

Answer 8

• Total time period during which is at risk of disease
• So death or development of disease means no longer qualify

Question 9

Advantages of cohort studies

Answer 9

 Sequence of events established
 Information about natural history
 Examine multiple outcomes
 Rare exposures can be studied
Useful for occupation exposures

Question 10

Disadvantages of cohort studies

Answer 10

 Slow and expensive
 Loss to follow up
 Exposure status can change

Question 11

Further disadvantages if retrospective

Answer 11

 Might lack info about confounding factors
 Can be difficult to identify exposed and not exposed groups

Question 12

Do cohort studies move from exposure to outcome or outcome to exposure

Answer 12

Always move forwards from exposure to outcome