Typicality Probability
Definition
In FORDISC analysis, the probability that the unknown skull is a typical member of the best-matching reference group, based on Mahalanobis distance. Values below 0.05 indicate the skull does not closely match any loaded reference group, often because the correct population is not represented. A critical output for honest population-affinity reporting.
- Cutoff value
- p < 0.05 typically indicates poor match to any reference group
- Used in
- FORDISC ancestry and sex estimation from skulls
- Foundation
- Mahalanobis distance from the reference group centroid
Common questions
What does typicality probability tell you in a skull analysis?+
Typicality probability shows how well an unknown skull matches a reference group in FORDISC analysis. It answers whether the skull is a typical member of the best-matching population. If the value is below 0.05, the skull does not fit any of the loaded reference groups well.
Why does a low typicality probability matter for identification?+
Low typicality signals that the skull is an outlier. This means the ancestry or sex probabilities from the same analysis may be unreliable. It often happens because the correct population is not represented in the reference data, not because the skull is unusual.
How is typicality probability calculated?+
It is based on Mahalanobis distance, which measures how far the skull is from the centroid of each reference group. A smaller distance means the skull is more typical of that group and produces a higher probability value.
Related terms
- FORDISC
- Forensic Discriminant Computer program, developed by Ousley and Jantz at the University of Tennessee Knoxville. Performs discriminant-function analysis on user-supplied craniometric measurements...
- Population Affinity
- The preferred modern forensic-anthropological term for the relationship between an unidentified individual's skeletal morphology and a modern reference population. Replaces the older...
- AABA 2020 Position Statement
- The American Association of Biological Anthropologists 2020 statement affirming that biological race does not exist as a discrete biological category in modern...
- Anterior Nasal Spine (ANS)
- A morphoscopic trait: the bony projection at the inferior border of the nasal aperture, scored on a 0-3 scale from absent to...
- Biological Race
- A concept from nineteenth-century physical anthropology that proposed discrete biological categories (races) of Homo sapiens. Modern population genetics and biological anthropology reject...
- BSA 2023 Section 39
- The expert-evidence provision of India's Bharatiya Sakshya Adhiniyam 2023, successor to Indian Evidence Act Section 45. Governs the admissibility of expert opinion...
- Caucasoid / Mongoloid / Negroid
- Nineteenth-century racial typological terms used in forensic anthropology reports through the 2010s. Discouraged by AABA (2020), SWGANTH (2013), and NIST (2020) because...
- Clinal Variation
- The pattern of continuous, geographically gradual change in a biological trait across human populations, without sharp categorical discontinuities. Human genetic and craniometric...
- Cranial Robusticity
- The overall size and prominence of bony surface features on the skull, reflecting body size and musculature. Males are on average more...
- Daubert Standard
- The US federal evidentiary standard (Daubert v. Merrell Dow Pharmaceuticals, 1993) requiring that expert testimony be based on scientifically valid methods with...
- Discriminant Function Analysis
- A multivariate statistical technique that derives linear combinations of measurements to maximally separate two or more groups (male and female). The resulting...
- Forensic Data Bank (FDB)
- The modern documented skeletal sample within FORDISC, built from cases submitted by US medical examiners since the late 1980s. Provides reference data...
Explained in these topics
- Ancestry from Cranial Morphology and FORDISCThe probability that the unknown skull is a typical member of the best-matching reference group, based on the Mahalanobis distance from that group's centroid....
- Sex Estimation from the Skull and MandibleA FORDISC output that indicates whether the skull being classified is morphologically similar to (typical of) the reference population. Low typicality (p < 0.0...
- The Modern Critique of Biological Race in Forensic AnthropologyIn FORDISC analysis, the probability that the unknown skull is a typical member of the best-matching reference group, based on Mahalanobis distance. Values bel...