# External validation

Source: https://onco.cc/terms/external-validation/  
OnCo record `external-validation` (Term). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

External validation tests a model on patients from a different hospital, country or platform than it was trained on; it is the only evidence that a result travels.

## Summary

External validity is the extent to which a study's conclusions generalise to other situations, people and times (Wikipedia). For a prognostic model that means an independent cohort, ideally collected by other people on another platform: TCGA-trained survival models are routinely tested on METABRIC, and the concordance index typically falls, sometimes to chance. A model with no external validation has an internal estimate, not a result, and several OnCo ideas argue that multi-site validation should precede clinical use.

## Fields

- Kind: Term
- Last checked: 2026-09-24
- Also known as: external validation; externally validated; external cohort; independent cohort; independent validation; external test set; generalisability; generalizability
- Tags: cansim-terms

## Notes

- Listed in the CanSim terms map 1.0.0 (docs/onco/terms.json, generated 2026-09-24), CC BY 4.0, attribution: CanSim project, an open, public-data-first cancer foundation-model programme; CanSim page path /terms/external-validation.

## Sources

- Wikipedia: https://en.wikipedia.org/wiki/External_validity
- Wikipedia: https://en.wikipedia.org/wiki/External_validity

## Connected records

- ideas: [A registry of external validation datasets for cancer AI models, with mandatory reporting](https://onco.cc/ideas/idea-tr2-ai-external-validation-registry/), [External validation at five or more sites in two countries before clearance](https://onco.cc/ideas/idea-data-multisite-validation-precondition/)
- terms: [Analytical versus clinical validation](https://onco.cc/terms/analytical-vs-clinical-validation/), [Calibration: reliability diagrams and the Brier score](https://onco.cc/terms/calibration/), [Cancer AI vocabulary (CanSim terms map)](https://onco.cc/terms/cancer-ai-vocabulary/), [Clinical covariates (age, stage, nodes, treatment flags)](https://onco.cc/terms/clinical-covariates/), [Cross-validation and stratified k-fold](https://onco.cc/terms/cross-validation/), [Domain shift and domain adaptation (cell line to patient)](https://onco.cc/terms/domain-adaptation/), [Drug-response data splits: leave-cell-line-out, leave-drug-out, leave-tissue-out](https://onco.cc/terms/drug-response-splits/), [Microarray expression data](https://onco.cc/terms/microarray-expression/), [Train, validation and test split discipline](https://onco.cc/terms/train-test-discipline/)

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JSON: https://onco.cc/api/v1/entities/external-validation.json