Bias & Misclassification Flashcards
What three aspects must researchers evaluate of their study (internal validity) before declaring a real and true association?
- Check for Confounding or Effect Modification
- Check for Bias
- Check for Statistical Significance
What is the definition of bias?
Systematic (non-random) error in study design of conduct leading to erroneous results
What does bias distort?
The relationship between exposure and outcome
What are the elements which bias has potential to impact?
- Source/Type
- Magnitude/Strength
- Direction
Is bias capable of accounting entirely for a weak association (RR/OR)? How about a very strong association?
- Yes
- No
Can bias over- or under-estimate the true measure of association?
Yes
Can bias have an enhancing or minimizing effect not eh true measure of association?
Yes
What are the two main categories of bias?
- Selection-related
2. Measurement-related
Define selection-related.
Any aspect in the way the researcher selects or acquires study subjects which creates a systematic difference between groups
Define measurement-realted.
Any aspect in the way the researcher collects information, or measures/observes subjects which creates a systematic difference between groups
What is measurement-related also known as?
Information/observation
What are the types of selection bias?
- Healthy-worker bias
2. Self-selection/participant (responder) bias
What is significant about the self-selection/participant (responder) bias?
Those wishing to participate may be different in some way to those that don’t volunteer/self-select to participate
What are the measurement subject-related biases?
- Recall
- Hawthorne effect
- Contamination
- Compliance/Adherence
- Lost to follow-up
What is Recall bias?
A different level of accuracy/detail in provided information between study groups
What is the Hawthorne Effect?
Individuals alter/modify their behavior because they are part of a study and know they are under observation
What is Contamination?
Members of the control group accidentally, or outside of the study protocol, receive the treatment or are exposed to the intervention being studied
What is Compliance/Adherence?
Groups being interventional studied have different compliance/adherence with study protocol/treatments
What is Lost to Follow-Up?
Groups being studied have different withdrawal or lost to follow-up rates or there are other differences between those that stay in the study and those that withdraw or are lost to follow up
Under what bias does differential vs. non-differential fall?
Lost to Follow-up
What are the observer-related biases?
- Interviewer
2. Diagnosis/Surveillance (Expectation)
What is the Interviewer bias?
The interviewer’s knowledge may influence structure and tone of the interview, which may in turn influence the response from the study subject
Interventions/treatments may not be applied equally between groups, can be conscious or unconscious actions of the interviewer
What is the 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 – a “Hawthorne-like” effect from the researchers’ perspective
What is the Screening-related bias?
Lead-Time
What is Lead-Time bias?
An apparent benefit from a healthcare screening due to the early detection of disease despite an unchanged clinical outcome
What is Misclassification Bias?
Error in classifying either disease or exposure status, or both
*Source of measurement (information/observation) bias
What is non-differential?
- Error in both groups, equally
- Misclassification of exposure or disease which is unrelated to the other (disease or exposure) depending on study design
What is the effect of non-differential?
For dichotomous variables, can move the measure of association (RR/OR) towards 1.0; it attenuates you effect estimates of association
What is differential?
- Error in one group differently than other
- Misclassification of exposure or disease is related to the other (disease or exposure) depending on study design
What is the effect of differential?
Bias can move the measure of association (RR/OR) in either direction in relation to 1.0; it can inflate or attenuate your effect estimates of association
How do you control for biases?
- Blinding/masking
- Use multiple sources to gather all information
- Randomly allocate observers/interviewers for data collection
- Build in as many methods necessary to minimize loss to follow-up
