Stochastic Threshold (ST)
Definition
A validated minimum peak height below which allele calls are considered uncertain due to stochastic amplification effects. Profiles with peaks between the analytical threshold and the ST require probabilistic interpretation.
- Definition
- Minimum peak height below which stochastic amplification effects make allele calls uncertain.
- Key issue
- Allele dropout and peak imbalance occur below this threshold, especially in degraded or mixture samples.
- Solution
- Probabilistic interpretation bridges the gap between analytical and stochastic thresholds.
Common questions
What happens when a DNA peak falls below the stochastic threshold?+
Allele calls become unreliable. Stochastic effects like allele dropout and peak imbalance make classical genotyping methods fail. These profiles require probabilistic interpretation instead of simple yes/no calls.
Why does the stochastic threshold matter in DNA mixtures?+
Mixtures with weak peaks below the ST can't be reliably sorted using standard methods. Probabilistic genotyping accounts for the uncertainty, letting forensic scientists work with the profile rather than discarding it.
How is the stochastic threshold validated in the lab?+
It's a scientifically validated minimum peak height set for each testing method. Labs establish it through analytical validation studies to define where their equipment's performance becomes unreliable.
Related terms
- Allelic Ladder
- A multi-allele reference standard containing the full range of known alleles at each STR locus in the panel, co-injected with samples to...
- Capillary Electrophoresis (CE)
- A separation technique that resolves DNA fragments by size through a polymer-filled glass capillary under an applied electric field. Single-base resolution is...
- Continuous Model
- A probabilistic genotyping approach that treats peak heights as a continuous variable and models their probability under different contributor genotype combinations, as...
- Drop-in
- Sporadic appearance of a low-level peak not reproducibly present in re-amplifications, typically caused by trace contamination. Distinguished from genuine minor-contributor alleles by...
- Drop-Out
- Failure of a genuine allele to amplify above the analytical threshold, typically due to low or degraded template. Creates apparent homozygosity at...
- EuroForMix
- An open-source continuous probabilistic genotyping platform developed by the Norwegian Institute of Public Health. Distributed as an R package and used by...
- GeneMapper ID-X
- Applied Biosystems analysis software for STR genotyping. Current-generation tool used in the majority of US, UK, and Australian forensic DNA laboratories.
- 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.
- Number of Contributors (NoC)
- The estimated minimum number of individuals whose DNA is present in a mixture, derived from the maximum allele count at any single...
Explained in these topics
- Capillary Electrophoresis and Electropherogram InterpretationA validated minimum peak height below which allele calls are considered uncertain due to stochastic amplification effects. Profiles with peaks between the anal...
- Mixture Deconvolution and Probabilistic GenotypingThe minimum peak height below which stochastic effects (drop-out, imbalance) make classical allele calling unreliable. Mixtures with peaks below the ST require...