[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Epidemiology](https://durgical.com/en/epidemiology/) › [Bias, confounding and causation](https://durgical.com/en/epidemiology/areas/bias/) › Bradford Hill criteria for causation

# Bradford Hill criteria for causation

- Concept

Nine viewpoints, proposed in 1965, for judging whether an association is causal. Only one is essential: the cause must come before the effect.

Updated Nov 5, 2026

## Key points

- Nine criteria: strength, consistency, specificity, temporality, gradient, plausibility, coherence, experiment and analogy.
- Temporality (the cause precedes the effect) is the only essential criterion.
- No single criterion proves causation.
- Specificity is the weakest: many exposures cause several diseases (tobacco, for example).
- They are applied after chance, bias and confounding have been ruled out.

## What it is

In 1965 Austin Bradford Hill proposed nine aspects for judging whether an observed association is probably causal: strength, consistency, specificity, temporality, biological gradient (dose-response), plausibility, coherence, experimental evidence and analogy. They are not a checklist to add up: they are questions that guide judgement after chance, bias and confounding have been ruled out. Temporality is the only one considered essential.

## Worked example

- Made-up case: an industrial solvent and liver disease in workers. The evidence is gathered criterion by criterion.
- Strength: pooled RR 2.2 across five studies.
- Consistency: the five studies, in four countries, give RRs of 1.8 to 2.6.
- Temporality: exposure precedes diagnosis by a median of 8 years.
- Gradient: RR 1.5 with under 5 years of exposure, 2.1 with 5 to 10 years and 3.0 with over 10.
- Plausibility and coherence: the solvent damages liver cells in animals and fits what is known of other liver toxins.
- Experiment: after extractor fans are installed, cases at the factory fall from 12 to 4 per year.
- Reading: with temporality met and nearly every criterion in favour, a causal relationship is very likely.

## The nine criteria

| Criterion | Question it asks |
| --- | --- |
| Strength | Is the association large (high RR or OR)? |
| Consistency | Is it repeated across studies, places and populations? |
| Specificity | Is the exposure linked to one particular outcome? |
| Temporality | Does the exposure come before the outcome? (essential) |
| Biological gradient | More exposure, more risk (dose-response)? |
| Plausibility | Is there a reasonable biological mechanism? |
| Coherence | Does it fit what is known of the disease's natural history? |
| Experimental evidence | Does removing or reducing the exposure lower the risk? |
| Analogy | Do similar exposures cause similar effects? |

## In practice

- These criteria are used in public health, occupational health and pharmacovigilance to judge whether a drug causes an adverse event.
- A strong association with a dose-response gradient is harder to explain by confounding alone.

## Common pitfalls

- Treating them as a checklist where adding up points is enough.
- Demanding specificity: one cause can produce many diseases.
- Dismissing a cause because no mechanism is known: plausibility depends on the knowledge of the day.

## Memory aid

Strength, Consistency, Specificity, Time, Dose, Plausible, Coherent, Experiment, Analogy: nine questions, and only Time is compulsory.

## Test yourself

Think of the answer, then tap the question to see it.

## Which Bradford Hill criterion is the only one considered essential?

Temporality: the exposure must come before the outcome.

## What is the biological gradient?

A dose-response relationship: the greater the exposure (dose, duration, intensity), the greater the risk of the outcome.

## Why is specificity a weak criterion?

Because many causes produce several diseases and many diseases have several causes; tobacco is the classic example.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/epidemiology/bradford-hill-criteria-for-causation/)

## Connections

## Related 5

- [Chance, bias, confounding or cause](https://durgical.com/en/epidemiology/chance-bias-confounding-or-cause/)
- [Reverse causation](https://durgical.com/en/epidemiology/reverse-causation/)
- [Confounding](https://durgical.com/en/epidemiology/confounding/)
- [Cohort study](https://durgical.com/en/epidemiology/cohort-study/)
- [Levels of evidence](https://durgical.com/en/epidemiology/levels-of-evidence/)

[← All of epidemiology](https://durgical.com/en/epidemiology/)

Educational content on epidemiological and statistical methods; the examples use made-up numbers to teach the calculation. Not a clinical or legal guide: current Colombian rules are in the official sources.

Sources: [Bradford Hill criteria | UMC](https://who-umc.org/signal-management/bradford-hill-criteria/) (Uppsala Monitoring Centre, 2026); [Chapter 14: Completing ‘Summary of findings’ tables and grading the certainty of the evidence](https://www.cochrane.org/authors/handbooks-and-manuals/handbook/current/chapter-14) (Cochrane, 2024).

## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake

Representative model, for educational purposes only.

---
Source: https://durgical.com/en/epidemiology/bradford-hill-criteria-for-causation/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/epidemiology/bradford-hill-criteria-for-causation/