2. Bias in General
• Bias: Any systematic error in the design, conduct
or analysis of a study
• Two different sources of bias:
(a) Approach used for selecting subject for a study
(selection bias)
(b) Approach used for collecting or measuring
data from a study (information bias)
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3. Information Bias
• Also known as misclassification
• Most common sources of bias that affects
validity of health research
• Originates from approach that is utilized to
obtain or confirm study measurements
• 3 specific forms of information bias:
1. Self-reporting bias
2. Measurement error bias
3. Confirmation bias
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4. 1. Self-reporting Bias
• Method that requires participants to respond to
the researcher’s questions without his/her
interference
• Example: questionnaires, surveys or interviews
• When self-reporting data are correctly utilized,
can help to provide a wider range of responses
than many other data collection instruments. For
example, self reporting data can be valuable in
obtaining subjects’ perspectives, views and
opinions
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6. 1 (a) Social desirability Bias
• Social desirability bias occurs when respondents give
answers to questions that they believe will make them
look good to others, concealing their true opinions or
experiences.
• It often affects studies that focus on sensitive or personal
topics, such as dietary intake, drug use, income, violence
or sexual behavior
• Examples:
Usage of drugs
Intake of alcohol consumption
Example: Times exercise in a week
Example: Sexual behaviour
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7. 1 (a) Social desirability Bias
How to overcome social desirability bias:
• Validate the self-reporting instrument before
implementing it for data collection, either internal or
external
• Internal validation- responses collected are
compared with other data collection methods, such
as laboratory measurements. Example: urine, blood
and hair analysis-validation used for drug testing
• External validation– medical record checks or
reports from family or friends
• Marlowe-Crowne Social Desirability Scale
• Martin-Larsen Approval Motivation score
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10. 1. (b) Recall Bias
• Also known as recall error
• Participants provided responses that depend on
his/her ability to recall past event
• Occurs in case control and retrospective cohort
• Using self-administered questionnaires
• Can underestimate/ overestimate effect of
association
• For example: a recall error in dietary survey may
result in underestimates of the association between
dietary intake and disease risk
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11. 1. (b) Recall Bias
How to overcome recall bias
Related to 4 factors:
(a) Length of the recall period
(b) Characteristics of the disease
(c) Patient/sample characteristics (e.g. age, accessibility)
(d) Study design (e.g. duration of study)
To minimise/eliminate:
(a) Short recall period is preferable
(b) Recall period stratified to participant demographics and frequency of events
they experienced
(c) Use of memory aids, diaries
(d) Interviewing of participants prior to initiating the study
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12. 1. (b) Recall Bias
Overcoming recall bias:
When not possible to eliminate recall errors Need
to obtain information on the error characteristics and
distribution Obtained from previous or pilot studies
Validation largely depends on biological testing or
laboratory measurements. However, they are:
(a) Costly
(b) Subject to measurement errors
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13. 2. Measurement Error Bias
• The observed measurements are different from
the actual values
• Also known as measurement error,
measurement imprecision, measurement bias or
instrumental error
• Causes:
(a) Device inaccuracy
(b) Environmental conditions
(c) Self-reported measurements
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14. 2. Measurement Error Bias
• If this error is ignored, the results are known as
naïve analysis which can be misleading, bias,
inconsistent/ inefficient estimators of regression
parameters and can cause poor inferences
about hypotheses and confidence intervals
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15. 2. Measurement Error Bias
Further divided into two types
(a) Systematic measurement error bias- The
observed measurements deviate from actual
values in a consistent manner
(b) Random measurement error bias- The
observed measurement deviate from true values
in an unpredictable manner
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16. 2. Measurement Error Bias
Adjustment to measurement error bias:
(a) Systematic measurement error bias-
Calibration methods
(b) Random measurement error bias-
Statistical software packages, e.g R Software
Package, Stata
Simulation extrapolation, regression calibration
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17. 3. Confirmation Bias
• Tendency to interpret new evidence as confirmation of one's
existing beliefs or theories.
• Also known as confirmatory, ascertainment, or
observer bias
• Investigation requiring human judgment is
subject to confirmation bias
• Methods to overcome:
o multiple independent check study
o use of blinding or masking procedures,
whether single- or double-blinded
o independent feedback and confirmation
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19. References
• Althubaiti, A. (2016). Information bias in health
research: Definition, pitfalls, and adjustment methods.
In Journal of Multidisciplinary Healthcare (Vol. 9, pp.
211–217). Dove Medical Press Ltd.
https://doi.org/10.2147/JMDH.S104807
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The Marlowe–Crowne Social Desirability Scale (MC–SDS) is a 33-item self-report questionnaire that assesses whether or not respondents are concerned with social approval
A study using the MC–SDS determined that social desirability has a significant impact on responses to questions involving drug, alcohol, and psychiatric problems
How do you score Marlow Crowne?
Items are scored through answering on a 'True' or 'False' basis. One point for yes and zero points for no. The total score is found from the sum of the true statements.
These scales are sought to measure individuals' tendencies to present themselves overly positive in self-reports, thus allowing to control for SD biases.
The MLAMS (Martin, 1984) assesses the degree to which respondents report that they engage in behaviors that reflect a desire to receive positive evaluations and social reinforcements and avoid negative evaluations and social punishments. Items refer to a number of dimensions in which concerns with evaluation and approval may arise, including being well-regarded, being liked, and making good impressions. The long, 20-item version of the MLAMS consists of 15 positively-worded and 5 negatively-worded items
Biological testing or laboratory measurements are one of the most credible approaches to validate self-reported data
Systematic measurement error bias: Consistently higher or lower than actual values
Random measurement error bias: Follow normal distribution or propotional to the measured amount
