Match Probability
Definition
The probability that a randomly selected person or object from the relevant population would produce evidence as similar as the crime-scene sample, given that they are not the true source. A low match probability increases the evidential weight of an observed match.
- What it measures
- Chance a random person or object matches the evidence
- Assumption
- The candidate is not the true source
- Effect of a low value
- Increases the evidential weight of an observed match
- Not limited to
- DNA; applies to any comparable trait
Common questions
Is a low match probability the same as proof of identity?+
No. It quantifies how rare the matching feature is in a relevant population, not the probability that the defendant is guilty, and treating the two as equivalent is a known reasoning error, sometimes called the prosecutor's fallacy.
What determines which population the probability is calculated against?+
The reference population should reflect who else could plausibly have left the evidence, such as a local, national, or trait-specific database, and choosing an inappropriate population can make the reported figure misleading.
Related terms
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- Rarity Estimate
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