DL: Bias Flashcards
What is bias?
Any trend in data the can lead to a conclusion that could be untrue
Systematic error in any part of the trial
What aspects of a study is susceptible to bias?
- Selection of subjects
- Performance of the trial
- Measurement of the outcome
4.Data collection - Data analysis
6.Data interpretation - Reporting the findings
What are the major categories of bias?
Selection and information
What is selection bias?
A distortion in the estimate of statistic of interest → method of selecting subjects in the treatment group and control group
What are the types of selection bias?
- Sampling
- Ascertainment
- Confirmation
- Publication
- Exclusion
What is sampling bias?
Some members of the target population are more likely to be selected from the trial over others
What is ascertainment bias?
Patients selected for a study are not representative of all classes in a population
Surveillance or detection bias
Identify the type of bias:
Emergency medicine study enrolled patients only during day time hours
Sampling bias
What is ascertainment bias?
Patients selected for a study are not representative of all classes in the population
Surveillance or detection bias
Identify the type of bias:
Obese patients are more likely to undergo medical examinations, blood tests, and imaging studies than non-obese people. If obese subjects were being compared to non-obese subjects for risk of certain cancers, early cancers would be more likely to be found in the obese group, causing an overestimate of the true association.
Ascertainment bias
What is confirmation bias?
Tendency to interpret new evidence as confirmation of existing beliefs
Favoring data that confirms existing beliefs
Identify the type of bias:
In 2015, former president of the National Lipid Association advocated
for statin use in the elderly. Cited one CT of statin therapy which reported a reduction in cardiovascular disease in the elderly. Ignored the other published CT of statin in elderly which reported no significant reduction.
Confirmation bias
What is publication bias?
Occurs when all trials are not published
What kind of trials are excluded with publication bias?
Those that fail to show an effect or that show harm
Interpret the funnel graph
What does a bias funnel graph look like?
What is exclusion bias?
Investigators apply different eligibility criteria to different groups (cases/controls or treatment/control)
Identify the type of bias:
In choosing controls Investigators excluded women who had had: cholecystectomy, thyroidectomy for thyrotoxicosis, surgery for renal disease, and any cardiac operation because, at the time, reserpine was one of the drugs often used in treating those conditions. The investigators feared that the prevalence of reserpine use in the controls would be artificially high
Exclusion bias
What is information bias?
Systematic measurement error or misclassification of the subjects into either risk factor or disease status
Measurement bias
What are the types of information bias?
- Recall
- Interviewer
- Observer
- Leas time
What is the main type of bias in case-control studies?
Information bias
What is recall bias?
Cases, people who have experienced an event, tend to try to identify some cause and thus are more likely to remember anything suggested as a cause
Exposures that people who did not
experience the event may not even notice
Identify the bias
Recall bias
What is interview bias?
Interviewers ask leading questions trying to clarify questions when clarification is not a part of study protocol
What is observer bias?
The observer may miss an event, diagnosis, or abnormality or think that one exists when it does not
Observer misinterprets data
Measurement is inaccurate or poor technique
Identify the bias
Repeatedly been documented in studies of blood pressure. Clinicians measuring participants blood pressure using mercury sphygmomanometers have beenfound to round readings to the nearest whole number.
Observer bias
What is lead time bias?
Distortion overestimating the apparent time surviving with a disease caused by moving the time of its diagnosis to an earlier time
Same outcome; exaggerated survival time
Identify the bias
Individuals with disease detected by screening receive a diagnosis earlier before signs and symptoms appear. As a consequence, estimates of differences in survival time between people diagnosed from screening and those whose disease is detected after symptoms develop can be biased, as survival time will appear to be longer in screen-detected people if early detection has no effect on the course of disease or if survival time is extended because of earlier detection.
Lead time bias
What is attrition bias?
Systematic differences between groups in
withdrawals from a study
Those who leave a study are likely to be different from those who continue.
Identify the bias
In an intervention study of diet in people with depression, those with more severe depression might find it harder to adhere to the diet regimen and therefore more likely to leave the study.
Attrition bias
What is maturation bias?
Occurs when we fail to account for what would have occurred if we done nothing
Any biological or psychological process within an individual that systematically varies with the passage of time, independent of specific external events (growing older, wiser, stronger, experienced, tired, hungry)
