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POPH192 > Module 4 > Flashcards

Module 4 Flashcards

1
Q

What questions does analytic epidemiology answer?

A

Is the exposure associated with the outcome? Does the exposure increase or decrease occurrence of the outcome?

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2
Q

What is PECOT?

A

Population - the group of people in the study
Exposure - what the potential determinant it
Comparison - what the potential determinant is being compared to
Outcome - the health outcome being assessed
Time - how long people are being followed up

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3
Q

What is relative risk?

A

How many times as likely is the exposed group to develop the outcome than the comparison group? The ratio of incidences

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4
Q

What is the formula for relative risk?

A

Incidence of exposed / Incidence of comparison

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5
Q

What is the RR when there is no difference?

A

1 (the null value)

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6
Q

What happens when the RR is more than 1?

A

The exposure is a potential risk factor for the outcome

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7
Q

What happens when the RR is less than 1?

A

The exposure is a potential protective factor for the outcome

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8
Q

What is risk difference also known as?

A

Attributable risk

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9
Q

What is the formula for risk difference?

A

Incidence of exposed - Incidence of comparison

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10
Q

What does the RD give?

A

How many fewer/extra cases of the outcome are attributable to the risk factor

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11
Q

What happens when incidence of exposed is the same as incidence of comparison (RD)?

A

Risk difference is 0 (null value)

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12
Q

What happens when incidence of exposed is greater than the incidence of comparison (RD)?

A

Risk difference is greater then 0 and the exposure is a potential risk factor

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13
Q

What happens when the incidence of exposed is less than the incidence of comparison (RD)?

A

Risk difference is less than 0 and the exposure is a potential protective factor

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14
Q

How is the risk difference interpreted?

A

There were (value) extra/fewer cases of (outcome) in (exposed group) compared to (comparison group)

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15
Q

How is the relative risk interpreted?

A

The (exposed group) were (value) times as likely to develop (outcome) compared to the (comparison group)

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16
Q

What are the differences between risk difference and relative risk?

A

Risk difference - impact of exposure and impact of removing exposure
Relative risk - clues to causes and strength of association

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17
Q

What may there be?

A

A weaker association but a bigger impact (small RR for common outcome) or a stronger association but a smaller impact (large RR for rare outcome)

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18
Q

Analytic Epidemiology…

A
  • Allowed by cohort studies
  • exposures and outcomes
  • causation
  • observation/intervention study
  • answers “WHY?”
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19
Q

What is a cohort study?

A

Observational: Observes exposures and what happens to them. Individuals are defined on the basis of presence or absence of exposure to a suspected risk factor

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20
Q

What can we measure from a cohort study?

A

Measures of occurrence - IP and IR

Measures of association - RR and RD

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21
Q

What are the strengths of cohort studies?

A
  • temporal sequence between exposure and outcome
  • examine multiple outcomes from an exposure
  • calculate incidence, RR and RD
  • good for rare exposures
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22
Q

What are the steps in a cohort study?

A
  1. Identify source population
  2. Recruit sample population (without outcome of interest)
  3. Assess exposure to identify which group participants belong in
  4. Follow up over time
  5. Observe whether participants develop the outcome
  6. Calculate measures of occurrence and association
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23
Q

What is the healthy worker effect?

A

When the exposure is specific to an occupation. Workers may be healthier than the general population so the comparison group must be considered carefully

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24
Q

What are limitations of a cohort study?

A
  • loss to follow up = bias if systematically different
  • misclassification of exposures/outcomes
  • not good for rare outcomes
  • time consuming
  • expensive
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25
Q

What must be considered when identifying source and recruiting sample in cohort studies?

A

Random selection independent of exposure status (classified after selection), rare outcomes may be selected based on exposure where an appropriate comparison group must be considered, be sure participants don’t have the outcome

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26
Q

What must be considered when assessing exposure in cohort studies?

A

Correct classification

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27
Q

What must be considered when following up in cohort studies?

A

Has exposure status changed? Loss to follow up? Length of follow up depends on incidence and how long disease takes to develop

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28
Q

What must be considered when observing development of outcome in cohort studies?

A

Correct classification of outcome

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29
Q

What happens in historical cohort studies?

A
  • existing data is used
  • reconstruct follow up period in the past
  • retrospective (look at outcome, classify based on exposure and follow over time)
  • good for rare outcomes
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30
Q

What are the strengths of historical cohort studies?

A
  • less time consuming than prospective
  • less expensive
  • good for outcomes that take time to develop
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31
Q

What are the limitations for historical cohort studies?

A
  • use existing data which the researchers have no control over the quality
  • might not be data about relevant factors
  • possible selection bias
32
Q

What are case control studies designed for?

A

Rare/slow to develop outcomes. Can efficiently examine acute or transient exposures

33
Q

What does a case control study do?

A

Ascertains outcome status, then finds exposure (equal amounts of cases and controls)

34
Q

What is the logic of case control studies?

A

If cases and controls are a good representation of those in the source population, ratio of odds of exposure= association between exposure and outcome

35
Q

What happens when the odds of exposure is greater in cases?

A

The exposure is more likely in cases and therefore a potential risk factor

36
Q

What happens when the odds of exposure is greater in controls?

A

Exposure is more likely in controls and therefore a potential protective factor

37
Q

What may effect exposure measurement?

A

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

38
Q

Why is the odds measured for cases control studies?

A

Because the number of cases and controls have been selected so can’t calculate incidence or prevalence

39
Q

What are the steps for case control studies?

A
  1. Identify source population
  2. Identify people with the outcome (cases)
  3. Sample people without the outcome from the 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)
40
Q

What happens in rare diseases for case control studies?

A

The odds ratio is approximately the relative risk so they are interpreted as the relative risk

41
Q

What are index dates used for?

A

To define the outcome for controls (pretend control had outcome on the same date)

42
Q

What must happen in case selection?

A
  • define by outcome (only one)
  • clear outcome definition and identification
  • comprehensive case finding
  • usually try and find incident cases but sometimes recruit prevalent
43
Q

What must happen in control selection?

A
  • Needs to represent the exposure distribution in the source population
  • must be capable of becoming a case
  • select multiple controls per case for statistical power
  • hospital controls aren’t usually representative
44
Q

What are the strengths of case control studies?

A
  • rare outcomes
  • transient exposures
  • multiple exposures
  • temporal sequencing
  • usually quick and inexpensive
45
Q

What are the limitations of case control studies?

A
  • study one outcome
  • difficult to select appropriate control group
  • susceptible to selection and recall bias
46
Q

What are the essential elements of a RCT?

A

Participants randomly allocated to groups, always have a comparison (control) group, testing effects of a treatment/intervention

47
Q

What is involved in randomisation?

A
  • randomly assign participants to intervention or control
  • avoids confounding as the two groups will be comparable based on all factors except the intervention
  • unless differ by an unknown factor
48
Q

How is randomisation protected?

A

Concealment of allocation, intention to treat analysis and per protocol

49
Q

What happens in concealment of allocation?

A

Allocation sequence must be concealed otherwise the system could be found out and bias introduced

50
Q

What happens in intention to treat analysis?

A
  • even if the person didn’t act how they were supposed to in their assigned group, they must be treated and included as though they did
  • more accurately reflects real world intervention
  • problematic if missing data
51
Q

What happens in per-protocol?

A

analyse remaining in trial (bad) which loses randomisation (still useful for efficacy)

52
Q

What is a trial?

A

Participants are assigned to exposed or comparison groups/arms to see if the intervention increases or decreases the likelihood of the outcome

53
Q

What are the characteristics of randomisation/random allocation?

A
  • equal chance of participant being in either group
  • if enough people randomly allocated, should have the same proportion of confounder in each group
  • applies to known and unknown confounders
  • if done successfully, differences are unlikely to be due to confounding
54
Q

What happens in blinding?

A

People involved in the study are unaware what group the participants are in (it is important to say who is blinded)

55
Q

Why may blinding be difficult to achieve?

A
  • can be obvious which group participant is in

- safety concerns (if something happens)

56
Q

What is non-adherence?

A

Participants don’t do what they are supposed to do which can include what the other group is doing

57
Q

What are the variants of randomisation?

A

cluster- randomising whole subgroups

stratified/block - randomising within subgroups

58
Q

What are the advantages of RCT’s?

A
  • best way to evaluate an intervention
  • can calculate incidence, RR and RD
  • strongest design for demonstrating a causal association
59
Q

What is the hierarchy of evidence?

A
  1. RCT
  2. Cohort
  3. Case-control
  4. Cross sectional
  5. Ecological
    Depends on how well the study is conducted
60
Q

What are the ethical issues of RCT’s?

A

Need to have clinical equipoise - genuine uncertainty about benefit or harm of intervention
Unethical to:
- give known harmful intervention
- give interventions known to be less effective than current treatments
- waste resources and risk peoples wellbeing if the answer is already unknown

61
Q

What are the practical issues of RCT’s?

A
  • resource intensive
  • more likely to be successful with large numbers (time and money)
  • exposure needs to be modifiable
  • often a very select group of people included which affects generalisability
62
Q

What is ethics?

A

About values and norms. Is especially important in the health and life sciences as these are value driven

63
Q

What are the dangers of healthcare research?

A
  • process could be harmful
  • individuals involved may be vulnerable
  • benefits may be unfairly distributed
64
Q

What are the solutions to the dangers of healthcare research?

A
  • assess the benefits and risks and ensure the ratio is acceptable
  • be aware of potential vulnerabilities of participants
  • avoid or manage conflicts of interest
  • obtain informed consent from participants
  • consider how the benefits and burdens of the research should be shared across society
  • introduce regulations and processes to ensure all these happen
65
Q

What does informed consent require?

A
  • disclosure of the purposes, risks and processes of the study
  • reasonable efforts from the researcher to explain this information
  • the person is competent to give consent
  • absence of coercive factors
    SHOULD BE ONGOING AND IN WRITING
66
Q

What are the NEAC guidelines?

A
  1. respect for persons
  2. justice
  3. Beneficence and non-maleficence
  4. integrity
  5. diversity
  6. addressing conflict of interest
67
Q

What may vulnerabilities be?

A

Poorer, racial, religious, educated, older, cognitive impairment, prisoners, children, ill

68
Q

What is beneficence?

A

Has to hold some benefit to society

69
Q

What is non-maleficence?

A

Not hurting anyone

70
Q

What is justice?

A

Transparency, all people considered equal worth, efforts to make society equitable

71
Q

What are conflicts of interest?

A
  • when a person holds two or more incompatible interests
  • concerning when interests might compromise the values discussed
  • may be professionally, academically, politically or financially
72
Q

What are policies for balancing benefits and harms?

A
  • Awareness of costs and harms to participants (time, resources, coercive factors, opportunity cost)
  • strategies to address harms/costs
  • awareness of potential cultural sensitivities or interests
73
Q

What is clinical equipoise?

A

Experimental treatment only provided if the evidence for the experimental treatment is equal to that available for the standard treatment. The participant must not suffer any substantial disadvantage from being in the study

74
Q

When is ethical review required?

A

When using human participants or testing something different from the current practice

75
Q

What is in the NZ review process?

A
  • ministry of health: administers for health and disability ethics committees
  • ACART and ECART (Ethics & advisory Committees for Assistive Reproductive Technologies)
  • Institutions have their own committees
  • Prerequisite for public funding and publication in major health journals

POPH192 (6 decks)

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