Bradford Hill’s Criteria for Inferring Causality Alex Ashley for Peer Support

Why? Lots of easy marks for not much revision It’s easy to mark 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 Features Other Evidence Exposure / Outcome

9 Criteria Association Features Other Evidence Exposure / Outcome 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)

S C B A T D R Mnemonic Association Features Other Evidence Exposure / Outcome T D R

Mnemonic Some Stupid Children Can’t Be Arsed To Do Revision Association Features Some Stupid Children Other Evidence Can’t Be Arsed Exposure / Outcome To Do Revision

Haribo + Diabetes in Peer Support Students

Association Features Strength of Association Specificity of Association Consistency of Association A causal link is more likely with strong associations (RR or OR) Peer support students who eat Haribo are twice as likely to get diabetes A causal link is more likely when a disease is associated with one specific factor and vice versa The only way to get diabetes is to eat Haribo A causal link is more likely if the association is observed in different studies and different sub-groups Female peer support students who eat Haribo get diabetes too

Biological Plausibility Other Evidence Coherence of Theory Biological Plausibility Analogy A causal link is more likely if the observed association conforms with current knowledge We know high sugar diets can lead to insulin insensitivity A causal link is more likely if a biologically plausible mechanism is likely or demonstrated Cells fail to respond adequately to normal levels of insulin A causal link is more likely if an analogy exists with other diseases, species or settings Psychology students who eat Haribo have more cavities

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) Students didn’t have diabetes before they came to Peer Support A causal link is more likely if different levels of exposure to the putative factor lead to different risk of acquiring the outcome Students who eat the whole bag of Haribo get diabetes more often than those who pick out one or two 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 sitting at the tables with fruit instead of Haribo don’t get diabetes