Lecture 20 - Case-control Studies

Question 1

What are case-control studies for?

Answer 1

• address some cohort issues
• for rare and slow to develop outcomes
• efficiently examine acute or transient exposure

Question 2

How do case-control studies work?

Answer 2

• identify people with the outcome
• find people without outcome
• compare exposure likelihood beforehand

Question 3

What are the steps in a case-control study?

Answer 3

• identify source population
• identify people with outcome
• Sample people without outcome from same population
• Measure exposure prior to outcome in cases and controls
• Compare odds of exposure to calculate measure of association

Question 4

What is the odds ratio equation?

Answer 4

odds of exposure (cases) / odds of exposure (controls)

Question 5

Why do we use odds?

Answer 5

• measure of likelihood
• can’t calculate incidence

Question 6

How do we report odds ratio?

Answer 6

People with outcome are x
times as likely to have had the
exposure than people without
the outcome

Question 7

Null value for odds ratio?

Answer 7

1

Question 8

What is the rare disease assumption?

Answer 8

• when the disease is rare, OR is approximately RR
• can interpret OR like RR

Question 9

How do we calculate odds?

Answer 9

• cases with exposure / cases without exposure
• controls with exposure / controls without exposure

Question 10

What are index dates?

Answer 10

a specific point in time used as a reference in a study to define the start of a period or the timing of an event

Question 11

What is the case selection for case-control?

Answer 11

• try to identify incident cases
• only one outcome that is defined and identifiable

Question 12

How do we control selection for case-control studies?

Answer 12

• need to represent odds of exposure in people without the outcome in the source population
• must be capable of becoming a case
• often select multiple controls per case for statistical power

Question 13

What control selection methods are for case-controlled studies?

Answer 13

• population controls
• hospital controls

Question 14

What are the strengths of case-controlled studies?

Answer 14

• Rare outcomes, transient exposures
• Multiple exposures
• Temporal sequencing
• Often comparatively quick and
  inexpensive