25 Flashcards
(38 cards)
What is information bias?
“ Observation or information bias results from systematic differences in the way data on exposure or outcome are obtained from the various study groups”
Two ways data is collected in a study
- By participants
- Collected or measured by someone else
How can measurement error occur?
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
Measurement error
can be random or systematic
What effect might measurement error have in a descriptive study?
• Could over/underestimate prevalence
What effect might measurement error have in a analytic study?
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)
Two types of misclassification
- Non-differential misclassification
- Differential misclassification
Non-differential misclassification
There is measurement error but it is‘ Not different’ between the study groups e.g. exposed/comparison group, or cases/controls
Differential misclassification
There is measurement error but it is ‘Different’ between the study groups e.g. exposed/comparison group,
or cases/controls
Non-differential misclassification can only move RR…
Closer to the null
Examples of differential misclassification
-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
What kind of bias (information) is case control susceptible to?
Recall
what is recall bias
“ Systematic error due to differences in accuracy or completeness of recall to memory of past events or experiences”
What can recall bias to to the OR
- bring it towards or further from the null
How to minimise recall bias
- Objective measures
- Validate self-reported measures with other information
- Memory aids
Cohort studies what type of bias
Potential for misclassification of exposure and outcome exposure/outcomes
What kind of classification do we need to concider for cohort studies?
Have the participants been correctly classified
Has the outcome status been correctly classified
Cohort studies: Differential misclassification
• 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
How to Minimising interviewer/observer bias
- Clearly defined study protocol and measures
- Structured questionnaire and standard prompts
- Training of interviewers
- Blinding
RCT how called information bias occur and how can u minimise it?
• 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
How to minimise information bias when Collecting information from participants
Validated survey instruments
Validate using objective measure
How to minimise information bias with Measurement instruments
Use standardised equipment Use calibrated equipment
How to minimise information bias via Collecting information via interviewers/observers
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
Publication bias
“The result of the tendency of authors to submit, organizations to encourage, reviewers to approve, and editors to publish articles containing ‘positive’ findings…”
