STRmix™ Use in Certified U.S. Forensic Labs Continues to Grow

An increasing number of ANAB or A2LA certified forensic laboratories in the U.S. are now using STRmix™ – sophisticated forensic software capable of resolving mixed DNA profiles previously regarded as too complex or degraded to interpret – in casework, according to statistics recently compiled by STRmix™.

The new data indicate that 80% of certified U.S. labs are now live with STRmix™ in casework, are currently validating the software, or have purchased the software but have not yet started the validation process. The data assumes that organizations which have multi-lab systems but are not yet live will use STRmix™ in all of their forensic labs.

“STRmix™ has clearly become the most tested and used forensic software among U.S. labs due to its ability to produce usable, interpretable, and admissible DNA results in a wide range of criminal cases, including most prominently violent crime and sexual assault cases,” says John Buckleton DSc, FRSNZ, Principal Forensic Scientist at the New Zealand Institute of Environmental Science and Research (ESR) and one of the developers of STRmix™.

Dr. Buckleton notes that STRmix™ has also proven to be instrumental in helping to solve cold cases in which evidence originally dismissed as inconclusive was reanalyzed, helping to develop investigative leads and support exonerations in post-conviction cases.  

ANAB and A2LA are among the largest accreditation bodies in the world. ANAB (ANSI National Accreditation Board) is the longest established provider of accreditation based on ISO standards for forensic agencies in the U.S. A2LA (American Association for Laboratory Accreditation), meanwhile, is dedicated to the formal recognition of competent testing and calibration laboratories.  

The new data on STRmix™ use in U.S. forensic labs comes on the heels of a survey conducted by New Zealand’s Institute of Environmental Science and Research (ESR) which indicates that STRmix™ has been used in at least 308,352 cases worldwide since it was introduced nearly a decade ago. This includes 152,837 cases in North America, 23,700 in Europe (including the U.K.), and 131,815 in Australasia.

Approximately a third of the more than 190 organizations with STRmix™ worldwide participated in the ESR survey. STRmix™ is currently in use in the U.S., New Zealand, Australia, the U.K., Ireland, Canada, Finland, Switzerland, and Denmark.

STRmix™ works by assessing how closely multitudes of proposed DNA profiles resemble or can explain an observed DNA mixture. Relying on proven methodologies routinely used in computational biology, physics, engineering, and weather prediction, STRmix™ calculates the probability of observed DNA evidence by assuming the DNA originated from either a person of interest or an unknown donor. These two probabilities are then presented as a likelihood ratio (LR), inferring the value of the findings and level of support for one proposition over the other.

A new version of STRmix™, Version 2.9, was launched last fall. STRmix™ v2.9 contains a number of new features, including: the introduction of a batch maker mode, allowing multiple interpretations to occur simultaneously and database search templates; memory usage improvements, which are particularly significant in dealing with higher order DNA profile mixtures; and improvements to biological modelling calculations designed to improve the modelling of stutter peaks.

The success STRmix™ has enjoyed to date led the team behind its development to introduce two related products which when used in combination with STRmix™ complete the full workflow(external link) from analysis to interpretation and database matching:

• FaSTR™ DNA, expert forensic software which rapidly analyzes raw DNA data generated by genetic analyzers and standard profiling kits and assigns a number of contributors (NoC) estimate; and
• DBLR™, an application which when used with STRmix™ allows forensic laboratories to calculate millions of LRs in seconds, visualize the value of their DNA mixture evidence, and carry out mixture-to-mixture matches, now allowing kinship analysis.

A new version of DBLR™ – featuring improved modelling through the introduction of linkage, mutation, and F_ST to the Kinship module, and the ability to assign LRs within the Kinship module for single source profiles containing both STR and SNP loci generated using Next Generation Sequencing (NGS) technology – was introduced in December 2021.