What Does It All Mean? Deciphering the Scientific Gibberish to Get the Answers You Need – Did They, or Did They Not Contribute DNA?!
Quick Summary
DNA testing is not an exact science—while your job (and ours) would be a lot easier with DNA reports that provided a simple yes or no as to whether someone contributed DNA, we instead have to deal with statistics, which can be difficult to understand if you are not familiar with the language used.
Often, DNA reports need to be read very carefully and multiple times to notice some of the distinctions.
When in doubt, please seek advice from either the Prosecution Scientist or an Independent Expert for clarification on what a report/result actually means.
DNA reports can sometimes read like a primary school exercise in double negatives written by Dr. Seuss. This is because they are intended to convey a statistical representation, not a legal recommendation.
You aren’t expected to understand all the science underpinning the reporting, but having a clear understanding of the terms used is vital to ensure this critical piece of evidence is interpreted and used correctly.
Commonly Misunderstood Terms
LR Less Than One (<1)
LR stands for the Likelihood Ratio—the statistic most often used in a DNA report. A result greater than one (>1) supports that an individual has contributed DNA to the DNA profile, while a result lower than one (<1) indicates there is no statistical support for the individual’s contribution of DNA to the DNA profile. Often, the value provided is confusing because it can range into the billions either way and be presented in ways such as 0.1E-12.
STRmix™
This denotes that these calculations have been performed by the STRmix™ software—the leading forensic biology program.
“10,000 Times More Likely Mr Smith Is Not a Contributor”
There is some debate as to what point scientists should exclude an individual as being a contributor but, while that debate rages on, we continue to get statements like the one above. These are confusing for juries because they often don’t understand to what we are comparing the likelihood, as well as the inclusion of a double negative (“not”). As a general rule, if this statement shows a number less than 10,000, it should be independently reviewed.
“10,000 Support for H2”
These statements refer to the likelihood ratio contained within the report, with the 10,000 being the likelihood ratio, and H1 propositions being the Prosecution proposition, with H2 being the Defence proposition. In this example, it is 10,000x more likely the Prosecution proposition is correct, i.e., it is 10,000x more likely an individual contributed DNA. As with the comment above, anything less than 10,000 should be independently reviewed.
Excluded
More often than not, if you see this in a report, it means the individual has been excluded as being a contributor to the DNA profile obtained by the scientist comparing the evidentiary DNA profile to the reference DNA profile. While there is some debate as to when a scientist should exclude an individual, generally an exclusion is offered when the statistics are overwhelming (often in the realm of billions times more or less likely).
Final Thoughts
Overall, making sense of DNA reports can be challenging if you are unfamiliar with the terminology and structure of the reports in your jurisdiction. Please take the time to read the reports carefully and seek help if the results are not clear.
Regards,
Jae
Ready to Strengthen Your Defence?
Independent Forensic Services is led by Principal Forensic Scientist Jae Gerhard. With over 20 years of experience from crime scene to court, Jae is a highly experienced expert witness who offers unbiased, evidence-based, and easy-to-understand forensic opinion.
DNA Expert Witness Testimony
We’re passionate about ensuring forensic biology and DNA evidence is presented to the courts in an impartial, yet comprehensive manner, and that potentially misleading evidence isn’t relied upon. We also want our clients to understand the strengths and limitations of forensic evidence in their cases.
Independent
As an independent forensic service provider, we offer unbiased and impartial analysis. Our independence guarantees that our findings are based solely on scientific evidence, free from external influences. This objectivity is crucial in ensuring the credibility and reliability of our forensic reports.
Confidential
We understand the sensitive nature of forensic investigations. Confidentiality is a cornerstone of our services. We handle all cases with the highest level of discretion, ensuring that your privacy and the integrity of the investigation are maintained at all times.
Trusted
Integrity is at the heart of everything we do. We are committed to ethical practices and uphold the highest standards of honesty and transparency in all our investigations. You can trust that our findings are accurate, thoroughly vetted, and presented with complete integrity.
Professional
Our team adheres to the highest standards in forensic science, ensuring that every case is handled with the utmost care and precision. We strive for excellence in all our services, providing reliable and accurate forensic analysis.
Highly Experienced
Our team comprises forensic experts with extensive experience across various forensic disciplines. With years of practical experience and advanced training, our professionals bring a wealth of knowledge to each investigation. This expertise ensures that we deliver top-tier forensic solutions tailored to your specific needs.
Approachable
We work closely with you, offering guidance and support throughout the investigation, ensuring you feel confident and informed. Our team is approachable and dedicated to making the forensic process understandable and straightforward.
Get Started
Choosing Independent Forensic Services means partnering with a team that values professionalism, experience, approachability, independence, confidentiality, and integrity. Trust us to provide the forensic expertise you need to achieve justice.
How We Can Help You
With Independent Forensic Services, you gain access to a team of experts.
An Expert Team Lead by Jae Gerhard
Jae Gerhard is a Forensic DNA Expert and the Principal Forensic Scientist at Independent Forensic Services, bringing over two decades of frontline experience in forensic biology. She has worked on some of Australia’s most complex and high‑profile cases with the Australian Federal Police and New South Wales Police, as well as international disaster victim identification operations in Bali and Thailand.
Specialising in DNA analysis, STRmix™, biological fluid examination, and bloodstain pattern interpretation, Jae now works independently with criminal defence teams to review and challenge forensic evidence. Her mission is simple: to ensure the science presented in court is accurate, balanced, and truly understood.