Post on 22-Feb-2016
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BRADFORD HILL’S CRITERIA
FOR INFERRING CAUSALITYAlex Ashley for Peer Support
WHY? Lots of easy marks for not much revision
3, 4, 6 marks? Make or break that question
It’s easy to mark Don’t have to be a medic to mark it
It’s easy to discriminate between the good students and the poor ones You know it or you don’t Spot when they’re asking for it (and when they’re not) Get the words right
THREE GROUPS OF CRITERIA
Association
FeaturesOther
EvidenceExposure
/ Outcome
9 CRITERIAAssociati
on Features
Strength of Association
Specificity of
Association
Consistency of
Association
Other Evidence
Coherence of Theory
Biological Plausibility
Analogy
Exposure /
OutcomeTemporal Sequence
Dose Response
Reversibility
(Experiment)
MNEMONICAssociati
on Features
SSC
Other Evidence
CBA
Exposure /
Outcome
TDR
MNEMONICAssociati
on Features
Some
Stupid
Children
Other Evidence
Can’t
Be
Arsed
Exposure /
Outcome
To
Do
Revision
HARIBO + DIABETESIN PEER SUPPORT STUDENTS
Association
FeaturesStrength
of Associati
on
Specificity of
Association
Consistency of
Association
A causal link is more likely with strong associations(RR or OR)
A causal link is more likely when a disease is associated with one specific factor and vice versa
A causal link is more likely if the association is observed in different studies and different sub-groups
Peer support students who eat Haribo are twice as likely to get diabetes
The only way to get diabetes is to eat Haribo
Female peer support students who eat Haribo get diabetes too
Other Evidenc
eCoheren
ce of Theory
Biological
Plausibility
Analogy
A causal link is more likely if the observed association conforms with current knowledge
A causal link is more likely if a biologically plausible mechanism is likely or demonstrated
A causal link is more likely if an analogy exists with other diseases, species or settings
We know high sugar diets can lead to insulin insensitivity
Cells fail to respond adequately to normal levels of insulin
Psychology students who eat Haribo have more cavities
Exposure /
OutcomeTempora
l Sequenc
e
Dose Respons
e
Reversibility
(Experiment)
A causal link is more likely if exposure to the putative cause has been shown to precede the outcome (RCTs, cohort)
A causal link is more likely if different levels of exposure to the putative factor lead to different risk of acquiring the outcome
A causal link is very likely if removal or prevention of the putative factor leads to a reduced or non-existent risk of acquiring the outcome
Students didn’t have diabetes before they came to Peer Support
Students who eat the whole bag of Haribo get diabetes more often than those who pick out one or two
Students sitting at the tables with fruit instead of Haribo don’t get diabetes