Cohort/Case Control Studies

Question 1

Two types of analytical studies?

Answer 1

Observational and experimental.

Case control and cohort are under observational.

Experimental: RCTs

Question 2

Main different between cohort and case control?

Answer 2

Cohort: Prospective

Case control: Retrospective

Question 3

Define a cohort study , and how can cohorts be defined ?

Answer 3

Cohort study: Group of people with something in common. Outcome free population from which a disease eventually arises.

Cohort defined by:

• Gepgraphical Region
• Occupational group
• Exposure event (atomic bomb)
• Birth cohort (born in a given year)

Question 4

Which methods are used to assess exposure?

Answer 4

Self report (questionnaire, in clinic with interviewer)

Clinic measurements

Existing records

People must be followed up, with the outcome and death cause obtained.

Question 5

What is and how do you calculate a risk ratio?

Answer 5

RR = Likelihood to develop disease if you’re exposed compared to unexposed.

RR= Incidence in exposed / incidence in unexposed.

Incidence is A fraction- 9 affected in 30 people means an incidence of 9/30.

Question 6

How to interpret a risk ratio?

Answer 6

RR<1 The exposure if associated with a lower risk of the outcome

RR=1 The exposure is not associated with outcome

RR>1 The exposure is associated with high risk of outcome

Question 7

Advantages and Disadvantages of cohort studies

Answer 7

Advantages: 
Study multiple outcomes 
Temproal relationship between exposure and disease 
Good design for rare exposures 
Incidence can be calculated 

Disadvantages:
Inefficient for rare diseases 
Expensive and time consuming 
Loss of follow up- introduces bias 
Healthy worker effect may affect generalisability

Question 8

How do you calculate and interpret an odds ratio?

Answer 8

Odds of being exposure among cases /odds of exposure among controls

1= No association
>1 Positive association between exposure and disease
<1 inverse association between exposure and disease, or exposure is associated with reduced risk of disease

Question 9

Advantages and Disadvantages of case control studies?

Answer 9

Ad:
Study rare diseases
Relatively inexpensive
Quick to acquire results

Disadvantages:
Possible bias in control selection 
Bias in exposure assessment (recall bias)
Uncertainty of temporal relationship 
Cannot calculate disease incidence