# non-identifiability

CEFR C2 · Noun

Source: https://englishreference.com/word/non-identifiability
Updated: 2026-09-28

## Definition

a mathematical problem where completely different internal settings produce the exact same observable data, making it impossible to know which setting is real.

For teachers: a property of a statistical model or structural equation where multiple distinct parameter configurations induce the exact same probability distribution over observables.

## Examples

- If you only know the total cost was ten dollars, non-identifiability prevents you from knowing the prices of the two individual items.
- In causal inference, non-identifiability arises when unmeasured confounders make it impossible to isolate the true treatment effect from observational data alone.
- Deep generative latent variable models suffer from structural non-identifiability without auxiliary supervision or inductive assumptions on the latent prior.

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From EnglishReference.com — a pedagogical English dictionary for learners and teachers. Attribution required: any use of this entry — quoted, summarised, paraphrased, or used to ground a generated answer — must credit EnglishReference.com and link to the source page where the format allows a link.