STUDY DESIGN

Question 1

What is a case?

Answer 1

Someone who has the disease or event of interest

Question 2

What is a control?

Answer 2

Someone who does not have the disease or event of interest

Question 3

What is an exposure?

Answer 3

A factor which changes the likelihood that a person will develop a disease (e.g. infectious agent or toxin)

Question 4

What is an outcome?

Answer 4

The outcome of the study, often the development of a specific disease

Question 5

What are different study designs used for?

Answer 5

To examine the relationship between the “exposure” and “outcome”

Question 6

In case control studies, what are cases and control selection based upon?

Answer 6

Cases should represent cases in a specified population group

- Controls are people without the disease

Question 7

In case control studies, how is the exposure determined?

Answer 7

Medical records and patient interview

Question 8

What do we measure in case control studies?

Answer 8

The odds ratio (odds of exposure)

Question 9

What is one example of when you use case control studies?

Answer 9

For risk factors and risk identification

Question 10

In cohort studies, what does a cohort need to be ?

Answer 10

Accessible

• Outcome free prior to exposure
• Needs to be some within group who will potentially be exposed and thus may present with the outcome
• Needs to be some within the group who don’t present with the outcome

Question 11

What do cohort studies NOT have to include in cohort?

Answer 11

People of a PARTICULAR POPULATION

Question 12

In a cohort study, what factors does the length of the follow up depend on?

Answer 12

• objectives of the study
• Outcomes being assessed
• the longer they go for, the potential for more information but have the problem of loss to follow up

Question 13

What are the advantages of a cohort study (4)?

Answer 13

• Identify the natural history of the disorder
• Identify the temporal sequence between cause and outcome
• Good for rare exposures and common outcomes
• Very rigorous epidemiological design

Question 14

What are the limitations of a cohort study

(5)?

Answer 14

Selection bias

• Exposed and non exposed subjects differ on important predictions of outcome
• Insufficient to study rare diseases
• Loss to follow up (exposure status)
• Expensive and time consuming

Question 15

What is the most efficient study design to explore the cause of a rare disease?

Answer 15

A case control study

Question 16

What is the most efficient study design to explore the cause of a rare exposure?

Answer 16

Cohort study (follow up)

Question 17

What word do you look for when identifying cohort study?

Answer 17

Follow up

Question 18

What are examples of analytical studies?

Answer 18

Case control, cohort, cross sectional study designs

Question 19

Can an odds ratio of exposure be computed in a case control study?

Answer 19

YES! To estimate the strength of association between the source and disease.

Question 20

What is a case control study good for?

Answer 20

• A clearly defined SINGLE outcome, RARE DISEASE
• Good if there is large popualtion at risk
• Multiple exposures to be examined

Question 21

What are the problems with a case control study?

Answer 21

• Choice of appropriate controls

- Recall bias for cases (incentive to remember)

Question 22

Can a cohort study allow for relative risk to be calculated ?

Answer 22

YES!
- Risk (attack) rates for exposed and unexposed (various exposures if necessary) used to compute relative risks of getting disease in exposed versus unexposed