Bias Flashcards
Biases in SR & MA
Publication bias
Language bias
Duplicate data
Heterogeneity - statistical, clinical, methodological
Outdated studies
Berkson bias
study sample taken from a sub-population
e.g. health-conscious people are more likely to join a trial
Bradford Hill criteria
group of nine principles used in establishing evidence of a causal relationship between an exposure & an event
include strength, consistency, specificity, temporality
Definition of confounder
variable that influences both exposure & outcome in triangular fashion, causing a spurious association not demonstrating causality
Definition of selection bias
systematic differences between baseline characteristics of groups due to selective recruitment
Definition of performance bias
systematic differences in care provided to different study groups other than the intervention of interest
Definition of detection bias
systematic differences between groups in how outcomes are determined
Definition of recall bias
systematic error that occurs when participants do not remember previous events or experiences accurately or omit details
Definition of attrition bias
type of selection bias due to systematic differences in the number & way participants are lost from a study between study groups
Definition of publication bias
when the outcome of a research study biases the decision to publish or otherwise distribute it
What is bias
Factor which causes SYSTEMATIC over- or under- estimate of a particular result
Types of biases that can occur in the designing of the study?
Selection bias, volunteer bias, channelling bias
Biases that can occur when conducting the research?
Interview bias, recall bias, Hawthorne bias
Biases that can occur in writing and publishing the study?
Publication bias, confounding
What is confounding bias…?
Confounding is when you have an independent factor which is associated with both the exposure factor and the outcome of interest with the disease
How can you minimise confounding factors?
Minimise through:
stratification,
multivariate analysis,
subgroup analysis
randomisation
restriction of criteria
matching
What is internal validity and external validity?
Internal validity - accuracy of conclusions
External validity - generalisability of results
Membership bias:
Explanation: Included patients are already participating in a study so might be more likely to look after their health, see the benefits of research, and educate themselves about treatment.
Neyman/survival bias
Explanation of an example: Included patients who had to be alive months after the treatment, out-selecting those with more rapidly evolving conditions who may have realistic idea of the treatment effects
Examples of confounders:
Age, ethnicity, sex, comorbidities (DM, alcohol intake), past surgery, previous family history, drug history, etc.
Diagnostic purity bias
Comorbidity is excluded in the sample population, such that it does not reflect the true complexity of cases in the population
Neyman bias (survival bias)
There is a time gap between the onset of a condition and the selection of the study population, such that some individuals with the condition are not available for selection.
Volunteer bias
Individuals volunteer for studies but they differ some way from the target population e.g. they are more motivated to improve health
Lead-time bias
Screening/testing increases the perceived survival time without affecting the course of the disease
