Tiffany Roy

A major challenge in forensic DNA is ensuring results are communicated in a way that ensures they are being understood. A great deal of thought goes into crafting report templates for standardization and readability. We know, as experts, these reports are being consumed by justice partners, including law enforcement investigators, judges and magistrates, and lawyers. These people are tasked with making important decisions that affect the life and liberty of criminal defendants. In the United States, a common trend is to keep reports short and sweet. If longer explanations are required, those discussions are often left for testimony. Report brevity can leave some ambiguous terms open for interpretation absent further explanation.

The way we communicate science to our end users is vitally important. Legal decisions are being made based on reports before trial and our words during trial. In recognition of those important decisions, efforts must be made not only to convey the most important components of our results, but also aspects that are more nuanced that could lead a lay person to misunderstand the strengths and weaknesses of the evidence presented. To ensure full understanding, greater efforts must be made to prevent possible misunderstanding. One way this can be accomplished in forensic DNA reports and testimony is through transparency and intentional language.

In every DNA report, there are required elements. The FBI Quality Assurance Standards and ISO 17025 set forth minimum information that must be described in every report, like sample descriptions and loci tested. However, some of the more nuanced information is left up to the laboratory to decide what they want to describe and define in more detail. Language that has snuck into our lexicon from our exposure to the legal system is sometimes used as a matter of custom. One example of this is the phrase, “to a reasonable degree of scientific certainty.” The National Commission on Forensic Science recommended against its use in testimony and reports because it really has no meaning in science. As a community, forensic DNA analysts need to critically consider each word or phrase being used to describe results for clarity.

One example of a term that has high potential to mislead a lay person is the term “sperm fraction.” In forensic DNA, we use it to describe the resultant parts of the differential extraction process, ie “sperm cell fraction and non-sperm/epithelial cell fraction”. With more laboratories moving away from serology screening to Y screening methods in sexual assault cases, using the word “sperm” might mislead a layperson into thinking sperm were identified on a sample when it was not. Forward thinking labs have renamed the fractions and the process is being clarified in reports. One great example of a clarification from a US lab states,

“A differential extraction two separate processes. The first process isolates the portion of the sample that may contain DNA from nucleated epithelial cells, white blood cells or buccal cells, and is referred to as the F1 fraction. The second process isolates the portion of a sample that may contain DNA from spermatozoa and is referred to as the F2 fraction. The use of a differential extraction does not imply the presence or absence of spermatozoa.”

In courtroom testimony, it has become increasingly important not only the state clearly what the DNA results mean, but also what they do not mean. As labs move from binary interpretation models and frequentist statistics to probabilistic genotyping and Bayesian statistics, serious thought should be given in reports and testimony to making clear how the two are different to prevent association fallacies. One association fallacy which presents routinely in court is (commonly a lawyer) equating the magnitude of the LR with uniqueness. A simple way this can be avoided is by including language in reports that states clearly, “no likelihood ratio, of any magnitude, should be taken to imply the person being compared is the unique source of the DNA on the evidence.” In testimony, likelihood ratios are often put into perspective by lawyers referencing the population of the planet, which is approximately 7 billion. Analysts should make clear in testimony that the likelihood ratio has no relation to the population of the planet, and even when it far exceeds the population, it doesn’t mean the person compared is the source of the DNA.

As previously discussed in an earlier installment of Just Communications, analysts are frequently asked questions about how the DNA could have gotten onto the item. Lawyers pose hypothetical questions that frequently call for explanations of the case evidence, leaving the analyst to acknowledge a list of possibilities which may or may not be helpful to the court. Because most US laboratories operate on the sub-source level of the hierarchy of propositions, the results being reported answer only questions of who could be a potential contributor and not how the DNA came to be present on an item. To head off some of the questions about activities, analysts should consider including a statement in their reports and testimony that makes clear, “the reported results address propositions regarding who could be a potential contributor and they do not address propositions about how the DNA came to be on the item.”

These clarifications go a long way in heading off commonly encountered trouble spots where DNA results could be misinterpreted by lay people. Especially in courtrooms where analysts have little to no control over how their results are described by lawyers in opening and closing statements, making these clarifications in reports and testimony help to prevent misinterpretation and misuse of forensic DNA results. While we may not have control over what questions are being asked of us in court, we have wide latitude to define and describe terminology in our reports and conclusions. Words mean different things to different people, and it’s the onus of the analyst to ensure their results are understood fairly and accurately by the people tasked with determining guilt or innocence in a criminal court.