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Z YEAR 2 LMAP > Epidemiology 2.5 > Flashcards

Epidemiology 2.5 Flashcards

1
Q

How do you estimate risk on case control study?

A

estimate likelihood on having the exposure in those who have the disease relative to those that do not

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2
Q

How do you calculate the odds ratio?

A

odds of exposure among cases / odds of exposure among control

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3
Q

Where does outcome go?

A

top of table

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4
Q

Where does exposure go?

A

side of table

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5
Q

What are cohort studies?

A

Group of people without disease, observed over period time

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6
Q

What do you do in cohort studies?

A

Selective target population and asses target exposure

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7
Q

What is the defining charctersotc of cohort studies?

A

track people forward in time from exposure to outcome

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8
Q

Why might the population be smaller at the end of a cohort study?

A
  1. people die
  2. move away
    - depending on type of people enrolled or end doing, some people healthy, or developed disease interest or different one or died
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9
Q

How do you select target population?

A
  1. If want to study chronic disease associated with ageing, may want to restrict target population
  2. Exposure of interest may be rare so may need to target a specific population e.g. farmers for pesticides
  3. Should initially attempt to identify as many subjects as possible without invoking any restrictions as want study finding to be generalisable
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10
Q

How is a cohort assembled?

A
  1. By geographic region
  2. By occupation
  3. Based on disease
  4. By risk group
  5. Birth cohort
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11
Q

How are exposure defined?

A

=Multiple exposure often assessed as analysis want to be able to control for exposures
-Exposures must be well defined: can be binary or all individuals exposed but at different levels or continuous variable

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12
Q

What are ways to assess exposure?

A
  1. Self report
  2. Taking physical measurements
  3. Using existing records
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13
Q

How do you ascertain the outcome?

A
  1. Routine surveillance
  2. Death certificates
  3. Medical record
  4. Directly from participant
    - Method used to assassin outcome must be same for exposed and unexposed group
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14
Q

How do you calculate relative risk?

A

ncidence in the exposed / incidence in unexposed

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15
Q

What are historical cohort studies?

A

group of individuals form the cohort, with a distribution of exposures and outcomes which are measured contemporaneously or extracted from health records.

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16
Q

Why are historical cohort studies not great?

A

Greater risk of selection and information bias

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17
Q

How do you cope with loss to follow up?

A
  1. Be transparent: it’s critical that participants lost to follow up in a study are reported as such. Loss to follow up is almost unavoidable, but where large proportions of participants are lost, one must consider the quality of the study, and whether the loss represents a potential bias. You’ll learn more about bias later.
  2. Be conservative: if there’s the potential for the loss to bias away from the null hypothesis, then reporting the output statistic which biases towards the null is generally the more sensible course of action.
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18
Q

When is case control used?

A

outcome already determined but exposures not understood

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19
Q

When is cohort used?

A

only exposure are available when treating study

20
Q

When is historical cohort used?

A

exposures and outcome known at start of study

21
Q

What are the approaches for assessing whether an exposure is associated with an outcome?

A
  1. Experimental studies

2. Observational studies

22
Q

What are randomised controlled trials?

A

experimental studies which compare and assess the effectives of two or more treatments to see if one treatment is better than another e.g. drug or method of care just always comparative group which acts like a control

23
Q

How do you maximise the value of the trial?

A

-Choice of control

24
Q

Does the process of randomisation protect against bias?

A

No. e.g. incorrect analysis of data

25
Q

What is the major limitation of observational study design?

A

Observed groups. may differentiations in characteristics other than the variable of interest

26
Q

What is intention to treat analysis?

A

Process of statically analysing patients’ outcomes using the original groups to which they were allocated, irrespective of whether they took the medicine or not

27
Q

What happens if you loose patients?

A
  1. Must include in analysis
  2. If patients withdraw from trial, try to find out if they are alive at the end of the trial and what happened to them and you include them in you original group because they were randomised to do that, even if didn’t take the drugs or carry out instructions what they were supposed to
28
Q

What is allocation not determined by?

A
  1. Investigation
  2. Clinicians
  3. Participants
    - Allocation not predictable
29
Q

What are the steps of randomisation?

A
  1. Generation of the allocation sequence

2. Implementation of the allocation (allocation concealmen

30
Q

How do you generate allocation sequence?

A

Random numbers table, or computer software, as long as no of participants large enough - everything the same, only thing different drug A or Drug B

31
Q

How do you conceal allocation?

A

Sequentially numbered opaque envelops, clinical can not open in advance and make sure seal not broken

32
Q

What is central randomisation?

A

investigators telephone a central randomisations service which issues a treatment allocation - vital no selection bias

33
Q

Is it true that a randomised placebo-controlled double blinded trial always involves two study arms?

A

False can have three or more

34
Q

What are sources of bias in a trial?

A
  1. Patient being treated
  2. Clinical staff administering treatment
  3. Physician assessing the treatment
  4. Team interpreting results
35
Q

What is blinding?

A
  • One or more parties in trial kept unaware which treatment arm participants have been assigned to
  • To avoid conscious or unconscious bias in design and delivery of clinical trial
36
Q

What is single blinding?

A

one part (participants usually)

37
Q

What is double blinding?

A

participants and clinicians, prejudice removed and in double prevents performance and detection bias

38
Q

What is performance bias?

A

refers to systematic differences between groups in care that is provided, or in exposure to factors other than the exposure of interest
-e.g. May focus on group that was given drug

39
Q

What detection bias?

A

refers to systematic difference between groups in how outcome are determined
e.g. participants may receive more frequent exams and experimental tests with active drug so experimental group greater chance of positive outcome

40
Q

What can blinding of those who assess trial outcomes achieve?

A

reduce risk that knowledge of which intervention was received rather than the intervention itself affects outcome measurement

41
Q

Why is blinding helpful?

A
  1. Doctor or patent who trusts intervention may unconsciously or deliberately find or perceive a positive effect e.g. important when outcome subjective e.g. degree of post-operative pain
  2. Blinding can also help prevent withdrawals from studies which can lead to incomplete data
    e. g. if know aspirin and comes back with stomach would be like no you are eon aspirin get off it now but if don’t know just be like monitor you and come back in a week when it might go away
  3. If patient knows inferior drug likely to drop out
42
Q

What is important in calculating sample size?

A

Withdrawals and anticipated drop out rates

43
Q

What increases with increasing sample size?

A

power

44
Q

What is power?

A

ability to detect an effect or association if one truly exists - should be at least 80% or 90%

45
Q

What does a power of 90% mean?

A

A power of 90% if true difference between treatments is equal to what we planned then only 10% chance the study will not detect it

46
Q

When might it not be possible to blind?

A
  • if comparing surgical techniques
  • ethically impossible to blind patient
  • makes it more costly to keep things blinded
  • difficult if drugs require titration

Z YEAR 2 LMAP (11 decks)

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