Bias & Misclassification Flashcards
Bias Definition
Systemic (non-random) error in study design or conduct leading to erroneous results.
Distorts the relationship between exposure and outcome
3 Components of Bias
- Source/Type
- Magnitude/Strength
- Direction
2 Main Categories of Bias
- Selection Related
2. Measurement Related
Selection Related Bias
The way the researcher selects or acquires study subjects that creates a systemic difference between groups
Measurement-related Bias
Any aspect in the way the researcher collects information or measures/observes subjects which creates a systemic difference between groups
Types of Selection Bias
- Healthy-Worker Bias
2. Self-Selection/Participant (Responder) Bias
Healthy-Worker Bias
Can be seen in prospective Cohort studies
The healthy workers would be taken as part of the study and those who have worked there and died or became sick are not counted. Even though they may have gotten sick because of exposure on the job
Self-Selection/ Participant (Responder) Bias
Those that volunteer may be different in some way to those who don’t volunteer
3 Main Types of Measurement Bias
- Subject-Related
- Observer-Related
- Screening Related
Subject Related Biases
- Recall (Reporting) Bias
- Contamination Bias
- Compliance/Adherence Bias
- Loss to Follow-up Bias
Recall (Reporting) Bias
- differential level of accuracy/detail in provided info between groups
- Those exposed or diseased may have greater recall because they have a greater reason to. They may also exaggerate their responses
- Individuals can report effects differently because they are part of a study
Hawthorne Effect
Individuals report differently or change their behavior because they know they are being followed
Contamination Bias
Members of control group accidentally receive treatment or are exposed to the intervention being studied.
Compliance/Adherence Bias
Groups being interventionally studied have different compliances.
How well do the patients follow the instructions
Lost to Follow-up Bias
Groups being studied have different withdrawal rates.
The groups are no longer equal. Either in numbers or personal characteristics
Observer-Related Biases
- Interviewer (Proficiency) Bias
2. Diagnosis/Surveillance (Expectation) Bias
Interviewer (Proficiency) Bias
- Systemic difference in soliciting, recording or interpreting on the part of the researcher.
- The knowledge of the interviewer may influence structure, or tone, of questions or follow-up questions which may influence response from study subject
- Interventions/treatments not applied equally between groups due to skill to training differences of study personnel
Diagnosis/Surveillance (Expectation) Bias
- Different evaluation, classification, diagnosis or observation between study groups
- Observers may have preconceived expectations of what they should find in examination, evaluation or follow up
Screening-Related Bias Example
Lead-Time Bias
Lead-Time Bias
An apparent benefit from a healthcare screening due to early detection of disease. Despite unchanged clinical outcome.
Misclassification Bias
Error in classifying either disease or exposure status or both
- Non-Differential
- Differential
Non-differential
Misclassification of exposure or disease which is Unrelated to the other depending on study design
Effect: bias moves the measure of association closer to 1
Differential
Error in one group different than the other.
Misclassification of exposure or disease is related to the other, depending on study design
Effect: Bias can move in all directions
Controlling for Bias
- Blinding/Masking
- Use multiple sourced to gather all information
- Randomly allocate observers/interviewers for data collection
- Build in as many methods necessary to minimize loss to follow-up
