Verbal Equivalent Scale
Definition
A standardised mapping from LR ranges to descriptive phrases, such as the ENFSI scale: LR 10 to 100 corresponds to 'moderate support', LR 100 to 1000 to 'moderately strong support', and so on. The scale provides a consistent vocabulary across laboratories and disciplines.
- Example body
- ENFSI (European Network of Forensic Science Institutes)
- Example band
- LR 100 to 1000 = 'moderately strong support'
- Purpose
- Consistent vocabulary across laboratories and disciplines
- Field
- Evaluative reporting of likelihood ratios
Common questions
Why does a shared scale like ENFSI's matter across disciplines as different as DNA and glass evidence?+
Different forensic disciplines historically developed their own informal wording for evidential strength, which made it hard for a court to compare, say, a fingerprint conclusion against a fibre conclusion; a shared band-to-phrase scale lets a fact-finder interpret 'strong support' the same way regardless of which discipline produced it.
Does adopting a standard verbal scale remove the need to disclose the numerical LR?+
No, standards bodies that publish verbal scales still expect the numerical LR or the calculation basis to be available, since the verbal phrase is a communication aid for a lay reader rather than a substitute for the quantitative result an expert or opposing party may need to scrutinise.
Related terms
- Activity-Level Proposition
- A proposition about what happened. Example: 'The suspect handled the knife' versus 'The suspect never handled the knife.' Activity-level propositions require the...
- 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...
- Offence-Level Proposition
- A proposition about guilt. Example: 'The suspect committed the assault' versus 'The suspect did not commit the assault.' Forensic scientists must not...
- Prosecutor's Fallacy
- The error of treating the RMP (or its reciprocal) as the probability that the defendant is innocent, or as the probability that...
- Source-Level Proposition
- A proposition about the origin of material. Example: 'The DNA profile originated from the suspect' versus 'The DNA profile originated from an...