Class Characteristics
Definition
Features deliberately or systematically imparted to a group of items by design or manufacture, such as the calibre of a bullet, the pattern woven into a fabric, or the lug spacing on a tyre. These narrow the universe of possible sources but do not individualize.
- Type
- Shared, category-level feature
- Source
- Design or manufacturing process
- Evidentiary role
- Includes or excludes a category; cannot individualize
- Contrast
- Distinguished from individual characteristics, which can identify a single source
- Applies to
- Firearms, tool marks, bite marks, handwriting, shoe prints, fibres, blood groups, and more
Common questions
What are class characteristics?+
Class characteristics are features shared by all items produced by the same design or manufacturing process. A firearm's caliber, the number of lands and grooves in a barrel, a saw's teeth-per-inch count, and a shoe's brand and size are all class characteristics. They tell you what category or type something belongs to, not which specific item it is.
Why can class characteristics narrow a case but not close it?+
Because every item made by the same process shares those features. Matching class characteristics means the evidence is consistent with a category of objects, which can include or exclude suspects. To point to a single specific source, examiners look for individual characteristics, the random marks and variations that set one item apart from all others made to the same design.
Where do class characteristics show up in forensic evidence?+
They appear across many evidence types. In firearms, they include caliber, twist direction, and groove count. In tool marks, they cover working-surface width and grind angle. In bite marks, arch shape and general tooth size range are class characteristics. In handwriting, the letterforms taught by a particular school system count as class characteristics. In each case, the class features are just the starting point.
Related terms
- Individual Characteristics
- Surface features on a fired bullet or cartridge case that arise from random or unique events (tool wear, corrosion, service damage) and...
- AFTE Theory of Identification
- The Association of Firearm and Tool Mark Examiners' standard (1992, revised 2011) for reporting tool-mark comparison conclusions as Identification, Inconclusive, or Elimination...
- Comparison Microscope
- Two compound microscope bodies connected by an optical bridge that presents one half of each body's image in a single split eyepiece...
- OSAC (NIST)
- Organization of Scientific Area Committees for Forensic Science under the US National Institute of Standards and Technology; the successor body to SWGDOC,...
- PCAST 2016
- President's Council of Advisors on Science and Technology 2016 report 'Forensic Science in Criminal Courts', which assessed foundational validity of forensic disciplines...
- Physical Evidence
- Any tangible item or material that can help establish or disprove a fact relevant to a case. Distinguished from testimonial evidence by...
- Abjad
- A script system representing only consonants, with vowels supplied by context; Arabic, Hebrew, and Urdu are abjads. Most individualising forensic features lie...
- Abugida (Alphasyllabary)
- A script system in which consonant characters carry inherent vowels modified by diacritical marks; Devanagari, Bengali, Tamil, and Thai are abugidas.
- Acquired Characteristics
- Individual characteristics that develop after manufacture through use, wear, damage, or corrosion. A new shoe has only class characteristics; a worn shoe...
- AFTE Conclusion Scale
- Association of Firearm and Tool Mark Examiners scale: identification, inconclusive (subdivided A, B, C), elimination, unsuitable. The court-admissible vocabulary.
- Alphabet
- A script system in which individual characters represent individual phonemes; Latin, Greek, Cyrillic, and Korean Hangul are alphabets.
- Asperity
- A microscopic surface protrusion on a tool's cutting edge; each asperity produces a groove in the substrate when the tool slides, contributing...
Explained in these topics
- Bite Mark Analysis: Anatomy, Mechanism and PatternsFeatures of a bite mark that identify it as belonging to a category (human versus animal, adult versus child) rather than to a specific individual. Arch shape,...
- Bullet Striation Comparison and the Comparison MicroscopeFeatures shared by all specimens produced by a given manufacturing design: land count, groove count, twist direction, and twist rate. Matching class characteri...
- Class versus Individual CharacteristicsFeatures produced by design or manufacturing process, shared by all members of a production group. They narrow the source to a category but cannot uniquely ide...
- Forensic Examination of Firearms, Bullets, Shells and CartridgesFeatures common to a group of weapons of the same make and model. For bullets: caliber, number of lands and grooves, twist direction, groove width. Narrows the...
- Individuality, Identity and the Logic of ComparisonFeatures deliberately or systematically imparted to a group of items by design or manufacture, such as the calibre of a bullet, the pattern woven into a fabric...
- Multi-Script Handwriting: Latin, Devanagari, Arabic and CJKWriting features shared by all writers taught using the same pedagogical system; the departure from class characteristics is the raw material for individual id...
- Physical Evidence: Nature, Types, Collection and Chain of CustodyFeatures common to a group of items that allow categorisation but not single-source identification, for example shoe brand and size, ABO blood group, fibre typ...
- Sharp-Force Trauma: Cuts, Stabs, Chops and Saw-Mark AnalysisThe measurable features of a saw mark (TPI range, kerf width, wall angle, floor texture, breakaway spur) that allow classification to a type of implement witho...
- Stereo Microscope and Comparison MicroscopeFeatures of a tool mark or firearm impression that are shared by all tools or firearms of the same design or manufacture class, and thus cannot by themselves d...
- Tool Mark Evidence: Types, Comparison Principles and CollectionFeatures common to a category of tool: type, working-surface width, tooth count, grind angle, manufacturing geometry.
- Tool Marks: Fundamentals, Striations and ImpressionsGeneral tool-mark features determined by design specifications, shared among all tools of the same type and size; insufficient alone for individual identificat...
- What Forensic Science Is: Definition, Aim and ScopeFeatures shared by all items of the same manufacturing type or category, such as the calibre of a cartridge case. Class characteristics can include or exclude...