Verbal Likelihood Ratio (VLR)
Definition
The scale used by ENFSI and the UK Forensic Science Regulator for forensic comparison conclusions, running from 'No support for the proposition that the images show the same individual' to 'Very strong support for the proposition'.
- Standards bodies
- ENFSI and the UK Forensic Science Regulator
- Scale endpoints
- No support through Very strong support for same-individual proposition
- Field
- Forensic facial comparison reporting
- Basis
- Underlying likelihood ratio computed from comparison evidence
Common questions
Why is the VLR scale phrased around a specific proposition rather than a plain probability?+
Facial comparison evidence is evaluated against two competing propositions, such as the images showing the same person versus different people, and the VLR expresses how much more likely the observed evidence is under one proposition than the other, which is a different question from stating the probability that the images show the same person outright.
What distinguishes 'very strong support' from a definitive identification in facial comparison reporting?+
Even the highest VLR category communicates the strength of the evidence relative to the two propositions rather than certainty, since facial comparison, unlike some other forensic disciplines, does not currently claim individualisation, so examiners are expected to avoid language implying an absolute identification even at the top of the scale.
Related terms
- AFRS (India)
- Automated Facial Recognition System, the face recognition module within India's CCTNS, operated by the NCRB and used for searching against mug shots,...
- Deep Convolutional Neural Network (DCNN) Embedding
- The face descriptor produced by a neural network trained to map face images into a metric space where same-person images cluster together;...
- ENFSI BPM
- The ENFSI Best Practice Manual for Forensic Comparison of Speech (2015, rev. 2022); the operational standard for speaker comparison in European forensic...
- False Positive Identification Rate (FPIR)
- In 1:N identification, the rate at which a probe image of an individual not in the gallery generates a top-rank match. Critical...
- IPD Pixels
- Inter-pupillary distance measured in pixels, the primary resolution metric for face recognition; NIST FRVT finds reliable recognition requires approximately 50+ IPD pixels;...
- Morphological Analysis
- The systematic comparison of qualitative facial feature shapes from a standardised feature list; the primary method in ENFSI BPM facial image comparison,...
- NGI Face Component
- The face recognition module within the FBI's Next Generation Identification system, which searches a gallery of over 600 million images, including driver's...
- NIST FRVT
- The National Institute of Standards and Technology Face Recognition Vendor Testing programme, the primary independent benchmark for facial recognition algorithms, publishing ongoing...
- Photo-Anthropometry
- The measurement of anatomical facial landmark ratios (scale-invariant) from face images; sensitive to head pose differences and requires geometric correction for images...