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Pop health > Lecture 20 Case control study > Flashcards

Lecture 20 Case control study Flashcards

1
Q

Analytic studies types

A

observational

  • cross sectional
  • ecological
  • cohort
  • case control

intervention
- randomised controlled trial

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2
Q

Limitations of cohort studies

A

Can be inefficient with rare/slow to develop outcomes

Can be inefficient with transient/acute exposures

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3
Q

case control study

A

Designed for rare/slow to develop outcomes

Can efficiently examine acute or transient exposures

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4
Q

Cohort vs case-control studies

A

cohort
- Ascertain exposure status,
then find out outcome(s)

case-control
- Ascertain outcome status, then find out exposure(s)

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5
Q

Randomised controlled trials

A

Intervene in individual studies

drug trial

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6
Q

Cohort study Can be inefficient with rare/slow to develop outcomes

A

Follow up long time
Incidence low
Cancers

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7
Q

cohort study Can be inefficient with transient/acute exposures

A

Brief increase in risk of outcome

Injuries

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8
Q

in case control study

greater odds of exposure (cases)

A

exposure more common in cases

potential risk factors

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9
Q

In case control study

greater odds of exposure (controls)

A

Exposure more common in controls

Potential protective factor

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10
Q

Logic of case-control studies

If controls good representation of source population

A

Ratio of odds of exposure may indicate association between exposure and outcome

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11
Q

In case controlled study the case is

A

Defined by only one outcome (cohort has multiples)

Define outcome clearly

  • Dont want people who like they have outcome but dont
  • Introduce bias
  • Eg death from alzheimer’s vs dementia

Comprehensive case finding

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12
Q

Prevalent cases

A

Association of developing disease (outcome) and association of how long have it

Survival or lack of cure with it

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13
Q

in case control

Relevant exposure period

A

Just before the outcome

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14
Q

in case control

Irrelevant exposure period

A

Right at the beginning of the follow up

Won’t affect the risk

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15
Q

Case controlled study allows

A

Look at relevant exposure period

Because we get people who’ve had the outcome and look before it

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16
Q

Odds of exposure in cases

A

People with exposure / people without exposure

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17
Q

Odds of people in control

A

People in controls with exposure / people in controls without exposure

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18
Q

Measure of association

A

Odds ratio (not incidences)

How many times as likely cases are to have the exposure compared to controls

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19
Q

What is the null value for the odds ratio?

A

Null value for ratios = 1

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20
Q

calculate odds ratio

A

Odds of exposure in cases / odds of exposures in controls

21
Q

Relative risks and odds ratios

A

Interpret exactly same way

22
Q

OR when disease rare

A

Will approximate RR

23
Q

case control study

Can use RR interpretation

A

Exposed group
Value
Outcome
Comparison group

24
Q

case control

Null value 1 below

A

Protective factor

25
Q

case control

Above null value 1

A

Risk factor

26
Q

What happens in a case controlled study

A
  1. Identify Source Population
  2. Identify people with outcome (cases)
  3. Sample people without outcome from same population (controls)
  4. Measure exposure prior to outcome in cases and controls
  5. Compare odds of exposure to calculate measure of association (odds ratio)
27
Q

Controls don’t have outcome

So when do you measure exposure for controls?

A

Can’t measure exposure just prior to outcome because by definition dont have it

Index dates

28
Q

Index dates

A

Point define when the controls had the outcome

29
Q

control case

Why use odds?

A

Can’t calculate prevalence or incidence of outcome

Have selected number of people in study with and without outcome

30
Q

Measure of association for case-control studies:

A

odds ratios

31
Q

Interpreting the odds ratio

Different interpretation to the RR

A

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

32
Q

interpret RR

A

People with exposure are x times as likely to develop the outcome as people without the exposure

33
Q

When disease is rare,

A

OR approximates the RR (rare disease
assumption)

Can interpret OR just like RR

Use RR interpretation in this course

34
Q

case control interpretation

A

Expose group
value (x times as likely)
outcome
comparison group

35
Q

what are Index dates?

A

Pretend control had event on same date as case (or close to it)

36
Q

Case selection:

important points

A

Defined by outcome, so only one

Clear outcome definition and
identification

Comprehensive case finding

E.g. Death from Alzheimer’s vs
death from dementia.
Routine data collections
Medical records

37
Q

Case selection:

prevalent cases

A

Usually try to identify incident cases

Sometimes just recruit people with the outcome (prevalent cases)

38
Q

Control selection:

important points

A

Need to represent the exposure distribution in source population
- Good representation of the odds of exposure in source population

Must be capable of becoming a case

Often select multiple controls per case for statistical power

39
Q

Exposure measurement:

important points

A

Need to measure exposure period before outcome

40
Q

Exposure measurement:

important points

A

Differential recall

Exposure measurement must be comparable

41
Q

Differential recall

A

Cases trying to work out what made them sick

Outcome may affect recall ability

42
Q

Exposure measurement must be comparable

A

Dead cases vs alive controls

Interviewers may act differently for cases and controls

43
Q

Cohort vs case-control studies

A

Cohort

- Ascertain exposure status, then find out outcome(s)

44
Q

case-control studies

A

case-control studies

- Ascertain outcome status, then find out exposure(s)

45
Q

Case-control studies

strengths

A
  • Rare outcome, transient exposures
  • Multiple exposures
  • Temporal sequencing
  • Often comparatively quick and inexpensive
46
Q

Case-control studies

Limitations

A
  • Usually can only study one outcome
  • Difficult to select appropriate control group
  • Can be susceptible to selection and recall bias
47
Q

General population

A

Ideal

- Most likely to represent the odds of exposure in source population

48
Q

Hospital controls

A
  • Looking at serious outcome tends to lead to hospital treatment
  • Convenient (know where they’re gonna be)

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