Verbal Equivalence Scale
Definition
A table that assigns a verbal phrase to a range of LR values or log10(LR) values. The phrase is used in written forensic reports to communicate evidential strength to non-specialist readers. The table itself must be defined and justified by the issuing laboratory or standards body.
- Function
- Maps LR or log10(LR) ranges to descriptive verbal phrases
- Purpose
- Communicates evidential strength to non-specialist report readers
- Governance
- Defined and justified by the issuing laboratory or standards body
- Field
- Evaluative forensic reporting
Common questions
Why can't every laboratory just use its own informal wording for evidential strength?+
An undefined or inconsistent verbal scale risks a reader interpreting phrases like 'strong support' differently across cases or laboratories, undermining comparability, so standards bodies require the mapping between LR ranges and phrases to be explicitly documented and applied consistently within an organisation.
What is the risk of relying on the verbal phrase alone without the underlying LR value?+
A verbal phrase compresses a numerical range into one category, so two cases with very different LR values near the boundary of a category could receive the same wording, which is why best practice is to report the phrase alongside the numerical LR or its range rather than the phrase in isolation.
Related terms
- ENFSI Guideline
- The European Network of Forensic Science Institutes Guideline for Evaluative Reporting in Forensic Science (2015, updated 2016). It defines the propositions framework,...
- Jeffreys Scale
- A logarithmic scale for Bayes factors proposed by Harold Jeffreys in Theory of Probability (1961). Levels run from 'barely worth mentioning' at...
- Likelihood Ratio (LR)
- The ratio of two conditional probabilities: the probability of the observed evidence given the prosecution's hypothesis (same source), divided by the probability...
- Log10(LR)
- The base-10 logarithm of the likelihood ratio, sometimes called the weight of evidence (following I.J. Good). A log10(LR) of 1 corresponds to...
- Transposition Fallacy
- The error of treating the probability of the evidence given a hypothesis as though it were the probability of the hypothesis given...