Interpreting Epidemiological Findings (1) Flashcards
What are the terminology of Bradford hill criteria?
association vs causation
- criteria used to enable us to infer causation from observational and interventional methods
Strength Consistency Specificity Temporality Biological Gradient Plausibility Coherence Experiment Analogy
What does strength mean?
A stronger association increases the confidence that an exposure causes an outcome
What does consistency mean?
Consistent findings across settings tends to rule out errors or fallacies that might befall between studies
What does specificity mean?
describes an association between specific causes and specific events
If not specific – doesn’t mean invalidity! (esp. with multifactorial issues)
Specificity can be informative when present but its absence convey very little
What is temporality?
Measuring over time
the exposure should commonly precede the outcome
Hard to assess with cross sectional studies
What is biological gradient?
A dose-response effect is a compelling argument for causality
e.g. consuming more cigarettes increases likelihood of disease
What is plausibility?
Relationship should be biologically plausible where the science is understood
What is coherence?
The association ought to be consistent with the existing theory and knowledge
What is experiment?
Evidence from experimentation should be supportive of the proposed link
What is analogy?
Drawing upon analogous findings, we many make inference on the relationship
e.g. rubella causes deafness so you could consider that other viruses can cause similar issues
What is bias?
Any trends in the collection, analysis, interpretation, publication or review of data that can lead to conclusions that are systematically different from the truth
What are the three types of bias?
Selection
Information
Compounding
What is internal validity?
The extent to which findings accurately describe the relationship between exposure and outcome in the context of the study
-when association truly exists within study participants
What is external validity?
Generalisability
-when association observed within a study can be extended to the wider population
What can selection bias also be called?
What is selection bias?
How can you avoid selection bias?
Berkson’s bias – hospital based - case control study w/controls selected among the hospital’s patients
Healthy worker effect – active workers are more likely to be healthy than those who have stopped working (occupational studies)
Occurs when individuals or groups in a study differ systematically from target population leading to a systematic error in an association or outcome - When participation in a study is associated with the exposure and the outcome
to miminimse:
- Controls representative of target population
- Minimise non-response (i.e declining to participate)
- Compare respondents with non respondents
What is information bias?
Due to a number reasons we have misclassification of the exposure or disease status (or both)
Can include: interviewer, recall, response, and diagnostic bias
Due to ill-defined variables/flaws in data collection
Flaws in data collection
- Interviewer bias
- Recall bias
What is interviewer bias?
Interviewers ask about exposure status -
= Prevented by interviewer being blind/strict protocol when collecting data
Might be more thorough in interviewing on a related topic if disease status is known
e.g. smoking history in those with lung cancer
What is recall bias?
When people become ill they are more likely to think hard about how past experiences have affected them - – bias when participants self report exposures between cases and controls
= Prevent with objective ways to assess exposure
e.g. more likely to remember a brief period of smoking many years ago if you have been diagnosed with lung cancer
What is non-differential misclassification?
When exposure status is misclassified but equally among controls and cases
Errors in determining outcome in controls and cases
Bias always towards the null
What is differential misclassification?
Misclassification of exposure is not equal between cases and controls (disproportionate)
-Bias towards or away from the null
2 types of misclassification
non differential and differential
Key points
a. An epidemiologically sceptical approach requires us to rule out chance, bias (including
confounding) before we infer a real relationship – whether causal or not.
b. When assessing the validity of a study, we examine both its internal validity and its
generalisability (external validity) when interpreting findings.
c. There are nine Bradford Hill criteria that can be used to infer causality or absence
thereof. Their application is not a precise science but requires judgment and critical
thinking.
d. In addition to confounding, there are two major groups of bias: selection bias and
information bias.
e. Association does not equal causation.
which type of bias is described as Misclassification of the exposure, outcome or both.
information bias
the following are all types of which bias? Recall bias Response bias Interviewer bias Diagnostic bias
information bias
