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# The GRADE system

- Concept

GRADE rates how sure we are of an effect (high to very low) and keeps that certainty apart from the strength of a recommendation.

Updated Nov 5, 2026

## Key points

- Four levels of certainty: high, moderate, low and very low.
- Starting point: randomised trials at high; observational studies at low.
- Five reasons to rate down: risk of bias, inconsistency, indirectness, imprecision and publication bias.
- Three reasons to rate up: large effect, dose-response gradient and plausible confounding that would reduce the observed effect.
- Strong or conditional (weak) recommendation; low-certainty evidence can, in special cases, support a strong recommendation.
- Certainty is rated per outcome, not per study: the same body of evidence can be high for mortality and low for quality of life.

## What it is

GRADE is a system for rating the certainty of evidence for each outcome and for making recommendations. Evidence from randomised trials starts at high certainty and observational evidence at low; it is then rated down for risk of bias, inconsistency, indirectness, imprecision or publication bias, and rated up (mainly observational evidence) for a large effect, a dose-response gradient or plausible confounding that would work against the effect. A recommendation can be strong or conditional, depending on the balance of benefits and harms, certainty, values and resources.

## Worked example

- Data (made up): 4 trials with 2 400 patients; pooled RR for hospital admission 0.80 (95 % CI 0.62 to 1.03).
- Starting point: randomised trials, high certainty.
- Risk of bias: 2 of the 4 trials, carrying 55 % of the weight, did not conceal allocation: rate down one level, to moderate.
- Imprecision: the CI runs from a 38 % reduction (1 − 0.62) to a 3 % increase (1.03 − 1) and crosses 1: rate down again, to low.
- Inconsistency, indirectness and publication bias: no serious problems; final certainty low.
- Comparison: a cohort with RR 0.20 for another outcome starts at low and is rated up one level for a large effect, to moderate.
- Reading: the effect on hospital admission has low certainty; the panel issues a conditional recommendation.

## What lowers and what raises certainty in GRADE

| Lowers certainty | Raises certainty |
| --- | --- |
| Risk of bias | Large effect |
| Inconsistency between studies | Dose-response gradient |
| Indirectness (other population, other comparison) | Plausible confounding that would work against the effect |
| Imprecision (wide CI, few events) | — |
| Publication bias | — |

## Markers

- GRADE
- Certainty
- Strong
- Conditional

## In practice

- Clinical practice guidelines that use GRADE show the strength and the certainty of the evidence beside each recommendation.
- A conditional recommendation invites a decision with the patient: different people, with their values, would choose differently.

## Common pitfalls

- Mixing up certainty of evidence and strength of recommendation: they are two separate judgements.
- Rating a study instead of an outcome: GRADE rates the whole body of evidence for each outcome.

## Memory aid

Bias, Inconsistency, Indirectness, Imprecision and Publication pull down; Big effect, Gradient and Confounding against pull up.

## Test yourself

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

## At which certainty level does GRADE start evidence from randomised trials, and observational evidence?

Trials start at high and observational studies at low.

## What are the five domains that lower certainty in GRADE?

Risk of bias, inconsistency, indirectness, imprecision and publication bias.

## Which factors can raise the certainty of observational evidence?

A large effect, a dose-response gradient and plausible confounding that would work against the observed effect.

## Which kinds of recommendation does GRADE distinguish?

Strong and conditional (weak), for or against an intervention.

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## Connections

## Related 6

- [Levels of evidence](https://durgical.com/en/epidemiology/levels-of-evidence/)
- [Systematic review](https://durgical.com/en/epidemiology/systematic-review/)
- [Meta-analysis](https://durgical.com/en/epidemiology/meta-analysis/)
- [Clinical practice guidelines](https://durgical.com/en/epidemiology/clinical-practice-guidelines/)
- [Publication bias and the funnel plot](https://durgical.com/en/epidemiology/publication-bias-and-the-funnel-plot/)
- [Heterogeneity (I²)](https://durgical.com/en/epidemiology/heterogeneity/)

[← 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: [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, 2026); [WHO handbook for guideline development, 2nd Edition](https://www.who.int/publications/i/item/9789241548960) (World Health Organization, 2014).

## **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.

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Source: https://durgical.com/en/epidemiology/the-grade-system/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/epidemiology/the-grade-system/