Teaching Old and New Dogs Mixture Tricks of the Future

Most forensic DNA analysts old and new have worked with scientists throughout the past that still wax nostalgically about the silver staining years (or other DNA methods that pre-date many of us).  Generally speaking, nearly all DNA training programs involve components of the ‘history of DNA’ that cover the methods that led us to where we are today.  We find ourselves again on the cusp of a major change in the way DNA is treated for casework, this time not in how the laboratory processing is handled, but rather what we do with the profiles once we obtain them.

Over the last several years, very public cases of issues concerning how mixtures are handled at various laboratories, the 2016 President’s Council of Advisors on Science and Technology (PCAST) report on forensic science in criminal courts and increases in sensitivity of our laboratory processing has made it abundantly clear that past methods for mixture interpretation can be improved upon. So what was the forensic industry’s response? A series of mixture interpretation software programs were released throughout the world varying in price, complexity, statistical approach and availability to the average forensic laboratory.



Written by: Rachel Oefelein, DNA Labs International



In 2015, DNA Labs International acquired a software license for the STRmix™ mixture interpretation software program produced by the Institute of Environmental Science and Research (ESR) in collaboration with Forensic Science South Australia (FSSA).  Prior to acquiring the software license, I attended a week-long training on the software in San Diego, CA in January of that year.  Returning to South Florida I had two huge tasks to tackle first on the road to bringing the software online at our laboratory, expand on my own knowledge and train the remainder of the senior DNA analysts at DNA Labs International that would be utilizing the software.

The initial training program provided by ESR was critical in developing a foundation for the concepts utilized by the software program.  Furthermore, it formulated the beginning knowledge that would be required to start the validation and implementation process, recognize which mixtures and sample types are ideal for STRmix™ analysis and begin to grow the confidence in the process that would be required to later testify.

However, a weeklong training was not a substitution for years of knowledge obtained from training and practicing in previous statistical analysis methods like random match probability (RMP) and combined probability of inclusion (CPI).  Preparing our training program for the additional analysts utilizing STRmix™ analysis and completing our internal validation was essential in helping to create a fuller understanding of probabilistic genotyping at our laboratory.  Additionally, the STRmix™ support team was crucial in explaining and aiding through any hiccups that we came across along the way.

Training of our initial probabilistic genotyping analysis team and future analysts utilizing the software include the training materials utilized by the STRmix™ training in San Diego, an extensive literature review of existing publications and manuals on probabilistic genotyping software, hands on analysis utilizing the software and an oral competency examination.  The hands on analysis incorporated profiles that were selected by each analyst where they had previously determined that a mixed profile was inconclusive or supported an inclusion or exclusion.  It was determined that a thorough oral competency examination would be more beneficial than a written examination to prepare the scientists for providing expert witness testimony in court on the topic of probabilistic genotyping.

The path from the initial training to the competency was just the beginning of the learning process.  It is necessary, especially with new technology, to incorporate additional training as part of the continuing education for a laboratory’s analysts.  Recent publications on the topic of probabilistic genotyping are routinely distributed to scientific personnel and/or incorporated into the annual literature review program in an effort to supplement the training process and keep our analytical team abreast of new topics for purposes of being informed for both casework and testimony. With every new decimal release or version release of the software, release reports are issued from the STRmix™ team. These release reports and all internal validation summaries from new releases are distributed to our analytical team.

Additionally, training materials and competencies are issued for each new version release and DNA profiling system release with the software.  Moving forward, new analysts will obtain the previous DNA analysis training program in addition to the probabilistic genotyping software training program.  Much like our silver staining predecessors, it is indispensable to understand where we came from to fully understand where we are now.

Understanding and knowing how to use probabilistic genotyping software is half the battle, an analyst must also be able to explain the new technology to their clients, i.e. police, attorneys and investigators; and present their findings in court in a manner that a jury can understand.  Prior to testimony, the analytical team at our laboratory often participates in a case review and covers sample questions often presented in court applied to that specific case.  When possible, appropriate court motions and testimony transcripts are shared and discussed among the analyst staff to help prepare for future testimony.  Furthermore, common analogies in describing the technology and frequently asked questions (from both clients and attorneys) are discussed in regular meetings as a means of sharing information and growing and developing as a team.

DNA Labs International produces and distributes training materials on request to their customers and offers extensive communication to clients explaining the changes in DNA analysis procedures. Additionally, in person and video trainings have been provided and/or scheduled for attorneys on a one-on-one basis and in a jurisdictional group setting; for example, the entire State’s Attorney Office for a county.  It is necessary that both the practitioner and the client understand any new technology.  Moving forward, the training process will continue to evolve internally in our laboratory, for our clients and for the general public.


Requests for additional information can be made via:

info@dnalabsinternational .com

ATTN: STRmix Inquiry