20

Question 1

Types of analytic studies

Answer 1

Question 2

Limitations of cohort studies

Answer 2

• Can be inefficient with rare/slow to develop outcomes
• Can be inefficient with transient/acute exposures

Question 3

Alternatives to the limitations of cohort studies

Answer 3

Historical cohort studies
Case-control studies

Question 4

What issues can case-control studies address that cohort studies can’t?

Answer 4

• Designed for rare/slow to develop outcomes
• Can efficiently examine acute or transient exposures

Question 5

Cohort studies vs case-control studies

Answer 5

COHORT:
Measure exposure status
Follow over time
Compare development of outcome (incidence)

CASE-CONRTOL
Identify people with outcome
Find people without outcome
Compare exposure likelihood beforehand (odds)

Question 6

Case-control studies diagram

Answer 6

Question 7

Logic of case-control studies

Answer 7

Is the exposure more or less likely in people with the outcome (cases) than without (controls)?

Question 8

Step by step of a CASE CONRTOL study

Answer 8

1. Identifying source population
2. Identify people with outcome (cases)
3. Same people without outcome from the same population (controls)
4. Measure exposure prior to outcome in cases and controls
5. Compare odds of exposures to calculate measure of association (odds ratio)

Question 9

In case-control studies what measure of association is used ?

Answer 9

Odds ratio

Question 10

Why is the odds ratio used

Answer 10

Can’t calculate incidence of outcome
Have selected number of people in study with and without outcome

Question 11

Odds are not a measure of ……

Answer 11

Occurrence

Question 12

Odds ratio features

Answer 12

Measure of association
- Ratio of odds instead of incidences
- How many times as likely cases are to have the exposure
compared to controls

Question 13

Interpretation of the odds ratio vs the relative risk

Answer 13

Question 14

WHEN A DISEASE IS RARE…

Answer 14

Fortunately… OR ≅ RR
- When disease is rare, OR approximates the RR ( rare disease
assumption)
- Can interpret OR just like RR

Use RR interpretation in this course???? Wtf does that mean?!!!?

Question 15

Interpreting the odds ratio - 4 key things

Answer 15

• exposed group
• value
• outcome
• comparison group
• use RR interpitation

Question 16

3. Sample people without outcome from same population (controls)
4. Measure exposure prior to outcome in cases and controls

Controls don’t have outcome so when do you measure exposure for controls?

Answer 16

Question 17

Case selection - wtf does any of this mean

Answer 17

Usually try to identify incident cases
Sometimes just recruit people with the outcome ( prevalent cases) Case-control studies defined by outcome
So only one per study
Really important clearly defined and readily identifiable

Question 18

Control selection

Answer 18

Need to represent the exposure distribution of 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 19

Exposure measurement

Answer 19

Exposure measurement must be comparable
- dead cases vs alive controls
- interviewers may act differently for cases and controls
- cases trying to work out what made them sick
- outcome may affect recall ability

Question 20

Case-control studies - approximate____

Answer 20

RR with OR (interpret the same way)

Question 21

Cohort vs case-control studies

Answer 21

Question 22

Strengths of case-cotrol study

Answer 22

Strengths:
- Rare outcomes, transient exposures
- Multiple exposures
- Temporal sequencing
- Often comparatively quick and inexpensive

Question 23

Limitations of case control study

Answer 23

• Usually can only study one outcome
• Difficult to select appropriate control group
• Can be susceptible to selection and recall bias

Question 24

RCTS and the hierarchy of evidence

Answer 24