The interpretation of an evidentiary DNA profile should not be influenced by information about a suspect's DNA profile (3-6). Each item of evidence must be interpreted independent of other items of evidence or reference samples. Yet forensic analysts are commonly aware of submitted reference profiles when interpreting DNA test results, creating the opportunity for a confirmatory bias, despite the best intentions of the analyst. Furthermore, analysts are sometimes exposed to information about the suspects, such as their history or motives, eyewitness identifications, presence or absence of a confession, and the like. Such information should have no bearing on how the results of a DNA test are interpreted, yet may compound an unintentional confirmatory bias. This bias can result in false inclusions under not uncommon conditions of ambiguity encountered in actual casework. It can also render currently used frequency statistics or likelihood ratios misleading.
These problems can be minimized by preventing analysts from knowing the profile of submitted references (i.e., known samples) when interpreting testing results from evidentiary (i.e., unknown or questioned) samples. The necessary filtering or masking of submitted reference profiles can be accomplished in several ways, perhaps most easily by sequencing the laboratory workflow such that evidentiary samples are interpreted, and the interpretation is fully documented, before reference samples are compared. A simple protocol would dictate a separation of tasks between a qualified individual familiar with case information (a case manager) and an analyst from whom domain-irrelevant information is masked.