Interpreting epidemiological findings Flashcards
What are the Bradford hill cirtiera?
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 of errors or fallacies that might befall between studies
What does specificity mean?
Specificity can be informative when present but its absence convey very little
What is temporality?
Measuring over time
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
eg 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
What is external validity?
Generalisiability
What can selection bias also be called?
Berkson’s bias (in hospitals)
Healthy worker effect (occupational studies)
How can you avoid selection bias?
Controls representative of target population
Minimise non-response
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)
What is interviewer bias?
Interviewers ask about exposure status
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
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
What does non-differential misclassification result in?
Bias always towards the null
What is confounding?
The effect of an extraneous variable that wholly or partial accounts for the apparent effects of the study exposure, or that masks an underlying true association
What can confounding lead to?
Biased estimates
How can you identify confounding?
Knowledge of the subject matter
Three conditions for confounding
Stratfication
What are the three conditions for confounding?
Associated with the exposure in the source population
Associated with the outcome in the absence of the exposure
Not a consequence of the exposure
Compare crude and adjusted estimates
Only one of the above is necessary
How do you conduct stratification?
Compare stratum specific estimates with the estimate you get when you analyse the date from the study
What after conducting stratification might indicate confounding:?
Pooled estimate is considerably different from what you expect from stratum specific estimates
What is effect modification?
where the magnitude of the effect of an exposure variable on an outcome variable differs depending on a third variable
How can you test for effect modification?
Breslow-Day test
Q test
Interaction terms in regression models
What is synergism?
The effect modifier potentiates the affect of the exposure
What is antagonism?
The effect modifier demeans the effect of the exposure
What are adjusted models used for?
Identification of potential confounding
And used to account for it
What is a crude model?
univariate analysis of exposure vs outcome
What does the crude model do?
simply looks at the impact of the exposure on the outcome – with no consideration of anything else
What is an adjusted model?
multivariate analysis of a range of exposures vs. outcome
What is multivariate analysis?
multiple potential exposures have been included. The inference is that the outputs of these analyses mean that holding all other adjusted variables equal, X is the association between exposure and outcome
What are other ways of naming crude vs adjusted models?
Hazard ratio (HR) vs Adjusted Hazard Ratio (Adj. HR) Odds ratio (OR) vs Adjusted odds ratio (AOR) Univariate model vs multivariate model
