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

Features

Other Evidence

Exposure /

Outcome

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)

MNEMONIC

Association

Features

S

S

C

Other Evidence

C

B

A

Exposure /

Outcome

T

D

R

MNEMONIC

Association

Features

Some

Stupid

Children

Other Evidence

Can’t

Be

Arsed

Exposure /

Outcome

To

Do

Revision

HARIBO + DIABETESIN 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)

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