Information Bias Flashcards
what is information bias?
observation of information bias results from systematic differences in the way data on exposure or outcome are obtained from the various study groups
how can measurement error occur?
- participants provide inaccurate responses
- if they are providing subjective information then it can have errors, however there are some things that can only be measured this way eg. pain)
- therefore, objective measures are better as they don’t require judgement or recall to be made - data is collected incorrectly/inaccurately
what affect might measurement error have?
measurement error can be random (lack of precision) or systematic (lack of accuracy)
In a descriptive study:
- high over/underestimate prevalence (of outcome or exposure)
- this is something to ask ourselves when we are considering information bias
In an 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)
what are the two types of misclassification and what do they mean?
Non-differential misclassification
- ‘not different’ between the study groups (measurement error is the same between groups)
- ‘when measurement error and any resulting misclassification occur equally in all groups being compared’
Differential misclassification:
- ‘Different’ between the study groups (measurement error that is different between groups)
- could be due to people in the two different groups recalling information differently (eg. when you are diagnosed with a disease you tend to think about why you may have got it, and therefore will be more likely to recall better because you have put some thought into it)
- or could be due to interviewers asking more probing questions of one group bc they know what group they have been assigned to
describe the potential cross sectional study sources of information bias
- could be present due to self reporting they exposure since it is measuring prevalence of outcome a one point in time (so they have to ask the people about their exposure bc they weren’t tracking them then)
describe the potential case-control study sources of information bias
one of its limitations is that it is susceptible to recall bias as they have to ask about their exposure since they are looking at the outcome (ie. the exposure already happened)
what is recall bias?
systematic error due to differences in accuracy or completeness of recall to memory of past events or experiences
What are the three steps to consider when looking at bias?
- Who does it affect?
- How does it affect them?
- What effect does they have on the measure of association?
How do you minimise recall bias?
- objective measures
- validate self-reported measures with other information
- memory aids
describe the potential cohort study sources of information bias
potential for misclassification of exposure/outcomes is one of its limitations
Problems of differential misclassification in cohort studies: if the classification depends on the other axis of interest
- if classification of exposure depends on outcome (can be an issue in historical cohort studies)
- if classification of outcome depends on the exposure (eg. an interviewer knew the exposure status and examined the outcome differently for those in the exposure group compared to the comparison group - interviewer/observer bias)
how can interviewer/observer bias be minimised
- clearly defined study protocol and measures
- structured questionnaire and standard prompts
- training of interviewers
- blinding
describe the potential randomised controlled trials sources of information bias and how to rectify them
bias could occur is knowledge of the treatment/exposure category influences the assessment of the outcome
- ensure there is blinding
Bias could occur if measurement are undertaken differently for different treatment groups
- ensure measurement undertaken the same way
how do you minimise information bias generally?
Collecting information from participants:
- validated survey instruments
- validate using objective measure
Measurement instruments:
- use standardised equipment
- use calibrated equipment
Collecting information via interviewers/observers:
- ensure blinding
- use objective measures
- use structures interviews and standardised ‘prompts’
- training of interviewers
*Clearly defined study protocol
*well-defined exposures, outcomes and other factors collected in the study
What is publication bias?
It is something that affects the collective literature on the topic, and means that not all studies on that particular topic may have been published
“The result of the tendency of authors to submit, organisations to encourage, reviewers to approve, and editors to publish articles containing ‘positive findings’…
