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When DNA Samples Are Complicated: Calculating Variation in Mixed Samples Interpretation

NCJ Number
Date Published
December 2022

DNA technology has come a long way. In the not-so-distant past, a fair amount of either blood or semen was needed to create DNA profiles. Now, with highly sensitive techniques, DNA can be picked up from just a few cells left behind. Current DNA technology is sensitive enough to analyze DNA samples that include contributions from more than one individual, or so called “DNA mixtures.” DNA mixtures have, however, proven difficult to interpret due to variation in methods, sample quality issues, and interpretation problems. National Institute of Justice-supported researchers sought to improve mixed DNA analysis, eager to understand the amount of interpretation variation that exists in the analysis of complex DNA samples, both within and between laboratories. They found that significant intra- and inter-laboratory interpretation variation exists, and inclusion of a known reference DNA profile has a marked positive effect on interpretability. The study results also indicated that although most labs could interpret two-sample mixtures, the majority had difficulty in interpreting three-sample mixtures.