Likelihood Ratio Reporting
Definition
A Bayesian framework for reporting paint-comparison conclusions, expressing the probability of the observed data given the hypothesis of common source versus the probability given different sources.
- Framework
- Bayesian, hypothesis versus hypothesis comparison
- Applies to
- Paint layer comparison conclusions
- Numerator
- Probability of the data given common source
- Denominator
- Probability of the data given different sources
Common questions
Why do paint examiners prefer likelihood ratios over categorical match statements?+
A categorical match implies a certainty the data cannot support. A likelihood ratio expresses the strength of support for common origin against an alternative, letting the factfinder weigh it alongside other evidence.
What limits reliable likelihood ratio reporting in paint cases?+
The ratio depends on a representative database of alternative source paints. A thin or unrepresentative reference population weakens the denominator and can inflate or understate the reported strength.
Related terms
- ASTM E2937
- ASTM International standard guide for identification of paint binders by pyrolysis-GC-MS; specifies pyrolysis conditions, GC column, oven program, and diagnostic ion reporting.
- ATR (Attenuated Total Reflectance)
- An FTIR sampling mode in which the sample is pressed against a diamond or ZnSe crystal and the evanescent wave probes the...
- Backscattered Electron (BSE) Imaging
- An SEM imaging mode sensitive to atomic number and crystallographic texture; can reveal grain-boundary elongation patterns in the sub-surface cold-worked zone after...
- ENFSI EPG Protocol
- European Network of Forensic Science Institutes Expert Working Group on Paint protocol; the European standard for paint comparison examination sequence and reporting.
- FTIR Microspectroscopy
- Fourier-transform infrared spectroscopy collected from a microscope-focused spot of 10-20 µm diameter; the primary technique for paint binder characterisation.
- IRUG Database
- Infrared and Raman Users Group spectral database; covers historic pigments, artists' materials, and museum-object coatings. Primary reference for art-investigation paint analysis.
- Microtome Cross-Section
- A thin section of a paint chip cut perpendicular to the layer planes, allowing each layer to be examined separately by microscopy...
- Py-GC-MS
- Pyrolysis gas chromatography mass spectrometry. Thermal decomposition of a paint sample, separation of fragments, mass spectral identification. Definitive identification of polymer binders.
- Pyrogram
- The gas chromatographic trace of volatile fragments produced by pyrolysis of a polymer; acts as the polymer-class fingerprint in Py-GC-MS.
- Raman Microspectroscopy
- A vibrational spectroscopy technique using a focused laser beam to excite molecular vibrations in an ink sample. Non-destructive. Primary method for toner...
- SEM-EDS
- Scanning electron microscopy with energy-dispersive X-ray spectroscopy; provides elemental composition of each paint layer at 1-5 µm spatial resolution.