2016/09/09

Forensicmag September 9, 2016: Subjective DNA Mixture Analysis, Used in Thousands of Cases, Blasted by WH Panel

DNA mixtures can by mind-bogglingly complex. The genetic traces of more than two people can create statistical chaos indicating someone’s DNA is included, or excluded, from a sample – based simply on the judgment of the person doing the testing.

This chaos has been interpreted by mathematical forensic analysis. But it involves subjective estimations by trained experts.

Those estimates – called the Combined Probability of Inclusion – have been used in crime labs nationwide for decades. But that method of statistical analysis has no grounding in science – and needs to be overhauled, a controversial White House report now contends.

The President’s Council of Advisors on Science and Technology findings – known popularly as the PCAST report – instead backs computer programs with complex algorithms to interpret the mathematical riddles. But the report contends that even those tools need further scientific validation.

The report thereby questions potentially thousands of criminal cases, experts told Forensic Magazine.

“Subjective analysis of complex DNA mixtures, including with the widely-used Combined-Probability-of-Inclusion methods, is not foundationally valid,” the PCAST panel contends, “and objective analysis of complex DNA mixtures with probabilistic genotyping software is promising, but has not yet been sufficiently and appropriately validated and their limitations to be considered reliable for all complex mixtures.” more