Bias and Cofounding Flashcards
What is bias?
Bias refers to systematic error, meaning that multiple replications of the same study would reach the wrong answer on average.
What is the effect of bias on validity?
The concept of bias is the lack of internal validity or incorrect assessment of the association
When may bias be introduced?
- Literature review
- Sample specification and selection
- Executing experimental manoeuvre or exposure
- Measuring exposures and outcomes
- Data analysis
- Data interpretation
- Publication of results
What is a selection bias?
Arises from procedures used to select study subjects and from factors that affect study participation
What is the consequence of selection bias?
The relation between exposure and disease is different for those who participate in the study (the study population) and those eligible for inclusion (the target population)
What types of selection bias is there?
- Inappropriate definition of the eligible population
- Lack of accuracy of the sampling frame
- Uneven diagnoses in the target population
- During study implementation
How to deal with selection bias?
Choose a study population with care.
Maximise take up and follow up.
What is information bias?
Arises during data collection
What types of information bias exist?
- Observer (interviewer) bias
- Recall bias
- Reporting bias
- Hawthorne effect
- Detection bias
- Protopathic bias
What is observer bias?
An interviewer’s knowledge may influence the structure of questions and the manner of presentation, which may influence responses
What is recall bias?
Those with a particular outcome or exposure may remember events more clearly or amplify their
recollections
What is reporting bias?
Participants might give answers they perceive to be of interest to the investigators
What is the Hawthorne effect?
An effect first documented at a
Hawthorne manufacturing plant; people act differently if they know they are being watched
What is detection bias?
If greater effort is given to diagnosing disease in an exposed group than in an unexposed group
What is detection bias?
Exposure is influenced by early (subclinical) stages of disease
