STRmix v2.7 Released, Featuring Improvements in Resolving Profiles, Input Quality Checks

The latest version of STRmix™ – the sophisticated forensic software used to resolve mixed DNA profiles previously considered too complex to interpret – has been launched.

STRmix™ v2.7 builds on previous versions of STRmix™, while adding several key new features. These include the addition of a variable number of contributors (varNOC) for multi-kits and the ability to compare two or more DNA mixtures to find a common contributor.

“The new features that have been incorporated into STRmix™ v2.7 are in direct response to recommendations for improvements made by forensic labs to better address the on-the-job needs they regularly encounter,” says John Buckleton DSc, FRSNZ, Forensic Scientist at the New Zealand Institute of Environmental Science and Research (ESR).

Dr. Buckleton and fellow ESR scientist Dr. Jo-Anne Bright developed STRmix™ in collaboration with Dr. Duncan Taylor from Forensic Science South Australia (FSSA).

Other improvements offered by STRmix™ v2.7 include:

• The ability to vary the number of contributors in Hp and Hd in a varNOC run;
• The addition of quality checks to input files;
• Improved models for composite peaks; and
• Improved Markov Chain Monte Carlo (MCMC) models for sampling from a probability distribution.

The latest version of STRmix™ comes after a full year of technical development and testing.

Since its introduction in 2012, STRmix™ has been used to interpret DNA evidence in more than 100,000 cases around the world. It is currently being used by the forensic labs at 46 U.S. agencies, including the FBI and the Bureau of Alcohol, Tobacco, Firearms, and Explosives (ATF), and is in various stages of installation, validation, and training in another 60 U.S. labs.

“Forensic labs increasingly are turning to STRmix™ because it has greatly improved the usability of DNA to produce evidence in a wide range of criminal cases,” Dr. Buckleton explains. He notes that agencies using STRmix™ are reporting an increase of interpretable DNA in gun cases from about 40% to more than 70%. STRmix™ is also proving to be highly effective in delivering a significantly higher rate of interpretable results in sexual assault cases.

The previous update of STRmix™, issued in August 2018, featured a completely redeveloped and refreshed user interface which vastly improved usability and workflow. STRmix™ v2.6 also enabled a range of contributors to be entered when performing a deconvolution, while improving various aspects of the biological modelling.

The previous year, STRmix™ v2.5 was issued. That version included numerous features designed to significantly improve functionality, speed, and ease of use.

DBLR™, an application for calculating millions of likelihood ratios in seconds when used in conjunction with STRmix™, was introduced earlier this year. Likelihood ratios are used to assess the strength of DNA evidence and how likely it is that DNA found at a crime scene belongs to specific individuals.