Is DNA evidence reliable? There is no simple, or even meaningful, answer to this question. Placing the acronym “DNA” in front of the word “evidence” does not automatically confer any reliability status, bad or good. Forensic DNA evidence ranges from highly reliable to contentious, depending upon the nature of the evidence as well as the skill of the source laboratory and testimony of the expert witness. Testing errors and problems at one laboratory do not diminish the reliability of DNA evidence from another. In the same vein, an incompetent laboratory cannot use the good reputation of another facility to enhance its own credibility.
When dealing with a case involving DNA evidence, the relevant question needs to be – Is the DNA evidence and testimony in my case reliable? And the answer is, it depends.
- Was the testing performed at an ISO 17025 accredited laboratory audited to the (FBI) Quality Assurance Standards for DNA evidence? If not, there is likely no objective demonstration of the laboratory’s adherence (or not) to the relevant forensic quality standards, including proficiency testing, audits, validation, equipment calibration, documentation criteria and many other standards that work to ensure reliability.
- Did the forensic DNA evidence include an analysis of a complex mixture, or degraded profile? If so, there may be more than one possible interpretation of that profile and a reliable and fair conclusion should include a clear and comprehensive description of all possible interpretations, as well as the assumptions made to reach those conclusions.
- Did the forensic DNA evidence include an evaluation of the possibilities and probabilities of transfer and persistence of DNA in various case scenarios? Reliable DNA transfer and persistence evidence should be founded upon research data that reasonably encompass the hypotheses in your case; over-reliance on anecdotal data may undermine the reliability of this type of evidence.
An effective review includes an assessment of these kinds of reliability factors. Depending upon case- specific requirements, such a review usually needs to go beyond the case report to critically assess the underlying casework documents that form the basis of the final reports, and may also necessitate an assessment of the expert testimony and opinions.
Cecilia Hageman PhD, LLB, LLM – Forensic Biologist