32 Questions
What is bias defined as in the context of research?
A systematic error or deviation from the truth in results
What type of bias occurs when there are systematic differences in baseline characteristics between groups?
Selection bias
How can selection bias be avoided in RCTs?
By using randomization to minimize confounding variables
What is an example of selection bias?
Different ages of participants in the treatment and control groups
What is performance bias?
Unequal care between study groups
What is an example of performance bias?
Different oral-hygiene instructions for patients wearing self-ligating brackets vs. conventional brackets
Why is allocation concealment important in RCTs?
To prevent selection bias by concealing the allocation sequence from principal researchers
What is the purpose of effective randomization in RCTs?
To ensure comparability between groups
What is the purpose of blinding in a trial?
To prevent performance bias by making patients and clinicians unaware of the treatment
What is allocation concealment?
A way to conceal treatment allocation from the person randomizing the patient
What is attrition bias?
Bias due to participants dropping out of a study
When is blinding not possible?
In trials involving medical devices or surgery
What is the purpose of randomization in a trial?
To minimize differences between the treatment and control groups
What is the difference between single-blind and double-blind trials?
Single-blind trials blind patients, while double-blind trials blind both patients and clinicians
What is the purpose of concealment in a trial?
To prevent selection bias by concealing treatment allocation
Why is allocation concealment universally recommended?
Because it prevents selection bias affecting patient allocation
What is conflict of interest bias?
A situation where a professional's judgment is influenced by a secondary interest
What is an example of a non-financial conflict of interest?
A researcher seeking career advancement
What does the traffic light graph represent in a systematic literature review?
The risk of bias in each study reviewed
What does a red color in the traffic light graph indicate?
A high risk of bias
What is the purpose of assessing the risk of bias in a systematic review?
To identify potential sources of bias in each study reviewed
What is an example of a financial conflict of interest?
A company funding a trial of a drug produced by the same company
What is the main purpose of assessing bias in a systematic review?
To inform the reader about the quality of each study reviewed
What does a yellow color in the traffic light graph indicate?
An unclear risk of bias
What is a potential reason to exclude participants from a study after it has begun?
Failing to meet inclusion criteria
What is the purpose of recruiting more participants than needed for a sample?
To avoid attrition bias
What is detection bias also known as?
Assessment bias
Why is it important to blind outcome assessors?
To avoid detection bias
What is reporting bias related to?
Selective disclosure of information
When does reporting bias occur?
During the design, conduct, analysis, or dissemination of study methods
What is the primary goal of minimizing follow-ups in a study?
To reduce attrition bias
Why is it important to maintain detailed contact information for participants?
To get in touch with participants even if they move
Study Notes
Definition of Bias
- Bias is a systematic error or deviation from the truth in results.
- Biases can lead to underestimation or overestimation of the true intervention effect and can vary in magnitude.
Sources of Bias in RCT
Selection Bias
- Occurs when there are systematic differences in baseline characteristics between groups.
- Example: Selection of participants with differential age characteristics.
- How to avoid: Use randomization to minimize confounding variables and ensure comparable groups. Allocation concealment can also help prevent selection bias.
Performance Bias
- Occurs when there is unequal care between study groups.
- Example: An investigator who believes that self-ligating brackets collect less plaque and lead to lower plaque and periodontal index scores might follow patients with self-ligating brackets closer and offer more exhaustive oral-hygiene instructions.
- How to avoid: Blinding (single or double) can help prevent performance bias.
Attrition Bias
- Occurs when there is loss of participants from a sample after randomization (dropout).
- Attrition can lead to bias if the characteristics of participants with missing data are different between the randomized groups.
- How to avoid:
- Recruit more participants than needed for the sample (oversample).
- Provide compensation for attending every session.
- Minimize the number of follow-ups as much as possible.
- Make all follow-ups brief, flexible, and convenient for participants.
- Send routine reminders to schedule follow-ups.
Detection Bias
- Occurs when the outcome event is identified with different methods or criteria in the exposed and non-exposed groups.
- Also known as observer, ascertainment, or assessment bias.
- How to avoid: Blinding (or masking) outcome assessors.
Reporting Bias
- Occurs when there are systematic differences between reported and unreported findings.
- A distortion of presented information from research due to the selective disclosure or withholding of information by parties involved.
- How to avoid: Blinding (or masking) outcome assessors.
Conflict of Interest Bias
- A set of circumstances that creates a risk that professional judgment or actions regarding a primary interest will be unduly influenced by a secondary interest.
- Examples: Financial (e.g., a company funding a trial of a drug produced by the same company) and non-financial (e.g., career advancement, publishable results, service to patients or students, fame, power, or family and friendships).
Traffic Light Graph for Systematic Literature Review
- Red means a high risk of bias, yellow means an unclear risk of bias, and green means a low risk of bias.
- A useful tool for telling the reader your assessment of each study reviewed.
Learn about the definition and sources of bias in research, including selection bias, and how to avoid it in randomized controlled trials.
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