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POPH192 > 25 > Flashcards

25 Flashcards

1
Q

What is information bias?

A

“ Observation or information bias results from systematic differences in the way data on exposure or outcome are obtained from the various study groups”

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2
Q

Two ways data is collected in a study

A
  • By participants
  • Collected or measured by someone else
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3
Q

How can measurement error occur?

A

Participants provide inaccurate responses
• E.g. they may forget past exposures
• E.g. they may under or overestimate their exposure

Data is collected incorrectly/inaccurately
• E.g. problem with measuring device
• E.g. person collecting the data doesn’t follow the same procedure for all participants

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4
Q

Measurement error

A

can be random or systematic

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5
Q

What effect might measurement error have in a descriptive study?

A

• Could over/underestimate prevalence

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6
Q

What effect might measurement error have in a analytic study?

A

Can lead to misclassification

  • People without the exposure may be classified as having the exposure (and vice versa)
  • People without the outcome may be classified as having the
    outcome (and vice versa)
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7
Q

Two types of misclassification

A
  • Non-differential misclassification
  • Differential misclassification
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8
Q

Non-differential misclassification

A

There is measurement error but it is‘ Not different’ between the study groups e.g. exposed/comparison group, or cases/controls

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9
Q

Differential misclassification

A

There is measurement error but it is ‘Different’ between the study groups e.g. exposed/comparison group,
or cases/controls

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10
Q

Non-differential misclassification can only move RR…

A

Closer to the null

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11
Q

Examples of differential misclassification

A

-In a cross-sectional study, people with the outcome might report the exposure differently to those without the outcome

-In a case-control study, cases might more accurately recall past exposures compared to controls

  • In a case-control study, an interviewer who is aware they are interviewing a case might ask more probing questions about the exposure of interest

-In a cohort study, an interviewer aware of the exposure status may ask more probing questions about the outcome among those exposed compared with those in the comparison group

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12
Q

What kind of bias (information) is case control susceptible to?

A

Recall

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13
Q

what is recall bias

A

“ Systematic error due to differences in accuracy or completeness of recall to memory of past events or experiences”

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14
Q

What can recall bias to to the OR

A
  • bring it towards or further from the null
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15
Q

How to minimise recall bias

A
  • Objective measures
  • Validate self-reported measures with other information
  • Memory aids
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16
Q

Cohort studies what type of bias

A

Potential for misclassification of exposure and outcome exposure/outcomes

17
Q

What kind of classification do we need to concider for cohort studies?

A

Have the participants been correctly classified
Has the outcome status been correctly classified

18
Q

Cohort studies: Differential misclassification

A

• If classification of exposure depends on outcome
(BUT outcome not yet happened in a prospective cohort study; can be an issue in historical cohort studies)

• If classification of outcome depends on the exposure
E.g. if interviewer/observer knew the exposure status and examined the outcome differently for those in the exposed group compared with those in the comparison group

Interviewer/observer bias

19
Q

How to Minimising interviewer/observer bias

A
  • Clearly defined study protocol and measures
  • Structured questionnaire and standard prompts
  • Training of interviewers
  • Blinding
20
Q

RCT how called information bias occur and how can u minimise it?

A

• Bias could occur if knowledge of the treatment/exposure
category influences the assessment of the outcome
- Blinding

• Bias could occur if measurements are undertaken differently for different treatment groups
- Ensure measurements undertaken in the same way

21
Q

How to minimise information bias when Collecting information from participants

A

Validated survey instruments
Validate using objective measure

22
Q

How to minimise information bias with Measurement instruments

A

Use standardised equipment Use calibrated equipment

23
Q

How to minimise information bias via Collecting information via interviewers/observers

A

Blinding
Use objective measures
Use structured interviews and standardised ‘prompts’
Training of interviewers

*Clearly defined study protocol
*Well-defined exposures, outcomes and other factors collected in the study

24
Q

Publication bias

A

“The result of the tendency of authors to submit, organizations to encourage, reviewers to approve, and editors to publish articles containing ‘positive’ findings…”

25
Q

Three properties of a potential confounder

A
  1. Independently associated with the outcome
  2. Independently associated with the exposure
  3. Not on the causal pathway
26
Q

What can confounding do?

A
  • Over-estimation of a true association
  • Under-estimation of a true association
  • change direction of a true association (risk factor becomes
    protective)
  • give appearance of an association when there is not one (go
    from null to something else)
27
Q

Identifying potential confounders - if you don’t measure it, difficult to do anything about it later

A

Use literature to identify known and suspected risk factors for outcome (property 1)

Collect information on factors strongly associated with exposure, regardless if known risk factor (property 2)

28
Q

Controlling confounding in the study design

A
  • Randomisation
  • Restriction
  • Matching
29
Q

Controlling confounding in the study design
- Randomisation

A

Design study to minimise confounding by selection and allocation of participants

30
Q

Controlling confounding in the study design - Restriction

A

All attempt to make groups being compared alike with regard to potential confounder(s)

31
Q

What kind of confounders does randomisation eliminate and what study? - design phase

A
  • applies to known and unknown confounders
  • RCT
32
Q

Problems with using RCT to eliminate confounding

A
  • Works best with large sample size
  • Need equipoise
  • Need intention-to-treat analysis
33
Q

What does restiction mean? What kind of study designs?

A

Restrict sample to one stratum of potential confounde
Easy and can be applied to all study designs

34
Q

Problems with restriction

A
  • Can reduce generalisability
  • Reduces number of potential participants
  • Potential for residual confounding with imprecisely
    measured (or broadly defined) confounders
  • Usually only one potential confounder
35
Q

What is matching and what study can it be used in?

A

Choose people to make the control/comparison group have the same composition as the case/exposed group regarding the potential confounder.

Usually used in case-control studies

36
Q

Individual vs Frequency matching

A

Individual: Each case matched with one or more controls having the same confounding variable characteristic(s)

Frequency: matching at aggregated level

37
Q

Positives of matching

A
  • Useful for difficult to measure/complex potential confounders
  • Can improve efficiency of case-control studies with small numbers
38
Q

Cons of matching

A
  • Individual matching can be difficult and limit number of potential participants
  • Need special matched analysis for individual matching (Otherwise will under-estimate the measure of association)
  • Can’t assess association between potential confounder and
    outcome
  • Can’t assess whether truly a confounder

POPH192 (28 decks)

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