Number of Contributors (NoC)
Definition
The estimated minimum number of individuals whose DNA is present in a mixture, derived from the maximum allele count at any single locus in the profile.
- Also known as
- NoC
- Basic method
- Maximum allele count at any single locus
- Nature
- An estimated minimum, not a certainty
- Used in
- Mixture deconvolution, probabilistic genotyping
Common questions
Why is NoC described as a minimum rather than an exact count?+
Two or more contributors can share alleles at a locus, so the observed allele count may understate the true number of people present. A locus showing four alleles could come from two contributors who share no alleles, or from three or more contributors with overlapping genotypes, so NoC is a floor, not a fixed answer.
How does an incorrect NoC estimate affect a probabilistic genotyping result?+
Probabilistic genotyping software runs the deconvolution under an assumed NoC. If the assumed number is too low, the model cannot explain the full allele pattern and produces distorted likelihood ratios; if too high, it introduces spurious contributor possibilities. Analysts often test multiple NoC assumptions and compare model fit before committing to a value.
Can NoC be determined from a single locus?+
A single locus with a high allele count can set a lower bound, but reliable NoC estimation uses the maximum allele count observed across all tested loci, since any one locus may underrepresent the mixture due to allele sharing or dropout.
Related terms
- Continuous Model
- A probabilistic genotyping approach that treats peak heights as a continuous variable and models their probability under different contributor genotype combinations, as...
- EuroForMix
- An open-source continuous probabilistic genotyping platform developed by the Norwegian Institute of Public Health. Distributed as an R package and used by...
- LRmix Studio
- A semi-continuous probabilistic genotyping platform developed at Leiden University Medical Center. One of the first PG tools adopted by European forensic laboratories;...
- MCMC (Markov Chain Monte Carlo)
- A computational sampling method used by STRmix and TrueAllele to integrate the likelihood function over all possible contributor genotype combinations. Requires many...
- Mixture
- A DNA sample containing contributions from two or more individuals. Identified by the presence of more than two alleles at one or...
- Mixture Ratio
- The proportional representation of each contributor's DNA in the mixture, estimated from the relative peak heights of non-overlapping alleles across multiple loci.
- Probabilistic Genotyping (PG)
- A computational approach to mixture interpretation that models the entire electropherogram as a probabilistic output of a specified number of contributors, computing...
- Stochastic Threshold (ST)
- A validated minimum peak height below which allele calls are considered uncertain due to stochastic amplification effects. Profiles with peaks between the...
- STRmix
- A continuous probabilistic genotyping platform developed by ESR (New Zealand) and the Australian Federal Police. The most widely used PG platform in...
- TrueAllele
- A continuous probabilistic genotyping platform developed by Cybergenetics (Pittsburgh, PA). Used primarily in US criminal courts; available as a cloud-based service.