Study Designs - Lecture Nineteen Flashcards

Cohort Studies

1
Q

Cohort Studies step one

A

Identify a source population

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2
Q

Cohort Studies step two

A

Recruit your sample population

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3
Q

Cohort Studies step three

A

Assess exposure to identify which group participants belong to

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4
Q

Cohort Studies step four

A

Follow up overtime

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5
Q

Cohort Studies step five

A

Observe whether or not participants develop the outcome

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6
Q

Cohort Studies step six

A

Calculate measures of occurrence and measures of association

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7
Q

What can we measure using cohort studies?

A
Measures of occurrence
- Incidence proportion 
- Incidence rate
Measures of association
- Relative risk
- Risk difference
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8
Q

Incidence proportion

A

Number of people who develop the disease in a specific period / Number of people at risk of developing the disease at the start of the period

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9
Q

Incidence rate

A

Number of people who develop the disease in a specific period / Number of person-years at risk of developing the disease

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10
Q

Relative risk

A

How many times as likely it is that the exposed group will develop the disease compared to the comparison group
Rate ratio: IRe/IRc
Risk ratio: IPe/IPc

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11
Q

Risk difference

A

How many extra/fewer cases of the outcome there were in the exposed group compared to the comparison group
IRe-IRc
IPe-IPc

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12
Q

What might we need to consider carefully - Step One

A
  1. Identify a source population
    Ideal: random selection independent of exposure status
    Sometimes: Selection based on exposure status (might consider appropriate comparison group)
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13
Q

What might we need to consider carefully - Step Two

A
  1. Recruit your sample population

Can you be sure that the sample population does not already have the outcome?

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14
Q

What might we need to consider carefully - Step Three

A
  1. Assess exposure to identify which group participants belong in (exposed or not exposed i.e. comparison)
    Have participants been correctly classified?
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15
Q

What might we need to consider carefully - Step Four

A
  1. Follow up over time
    Have participants changed exposure status over time?
    Has everyone been followed up over the entire study? Otherwise lost to follow up
    How long do patients need to be followed up?
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16
Q

What might we need to consider carefully - Step Five

A
  1. Observe whether or not participants develop outcome

Has the outcome status been correctly classified?

17
Q

Strengths of cohort studies

A

Determine temporal sequence between exposure and outcome
Can examine multiple outcomes from an exposure
Can calculate incidence (and therefore relative risk and risk difference)
Good for studying rare exposures

18
Q

Limitations of cohort studies

A

Loss to follow up
Potential for misclassification of exposures/outcomes
Generally not good for studying rare outcomes
Time consuming
Can be expensive

19
Q

What could be done instead of cohort studies?

A

Case-control studies

Historical cohort studies

20
Q

Types of cohort studies

A

Prospective cohort studies

Historical cohort studies

21
Q

Prospective cohort studies

A

The research starts with classifying the exposure

22
Q

Historical cohort studies

A

The exposure and outcome have already happened

23
Q

Historical cohort studies strengths

A

Use existing data
Reconstruct follow-up period in the past
Less time consuming compared with prospective cohort studies
Less expensive
Good for outcomes the take a long time to develop

24
Q

Historical cohort studies limitations

A

The quality of existing data
May not know all relevant factors
Selection bias