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BRADFORD HILL’S CRITERIA FOR INFERRING CAUSALITY Alex Ashley for Peer Support.

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Presentation on theme: "BRADFORD HILL’S CRITERIA FOR INFERRING CAUSALITY Alex Ashley for Peer Support."— Presentation transcript:

1 BRADFORD HILL’S CRITERIA FOR INFERRING CAUSALITY Alex Ashley for Peer Support

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3 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

4 THREE GROUPS OF CRITERIA Association Features Other Evidence Exposure / Outcome

5 9 CRITERIA Association Features Strength of Association Specificity of Association Consistency of Association Other Evidence Coherence of Theory Biological Plausibility Analogy Exposure / Outcome Temporal Sequence Dose Response Reversibility (Experiment)

6 MNEMONIC Association Features SSC Other Evidence CBA Exposure / Outcome TDR

7 MNEMONIC Association Features SomeStupidChildren Other Evidence Can’tBeArsed Exposure / Outcome ToDoRevision

8 HARIBO + DIABETES IN PEER SUPPORT STUDENTS

9 Association Features Strength of Association 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

10 Other Evidence Coherence 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

11 Exposure / Outcome Temporal Sequence Dose Response 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

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