Error and bias in forensic behavioral science

A cri­sis is brew­ing in sci­en­tific psy­chol­ogy and foren­sic sci­ence. This con­cerns the over­all reli­a­bil­ity of all psy­cho­log­i­cal sci­ence (more on this later) and the qual­ity of expert evi­dence and tes­ti­mony in courts of law, regard­less of the expert’s dis­ci­pline (yes, even includ­ing the sup­pos­edly hard stuff, like DNA analysis).

The con­sen­sus: alarm­ingly poor. This is the opin­ion of National Academy of Sciences’ National Research Council Report, “Strengthening Forensic Science in the United States: A Path Forward.“
“The focus has shifted to include the eval­u­a­tion of meth­ods and tech­niques rather than sim­ply the expert’s inter­pre­ta­tion of the results” (Christensen et al, 2014, p. 123).

The con­cern here is the qual­ity of expert tes­ti­mony in high stakes sit­u­a­tions where the reli­a­bil­ity of judi­cial decision-making, indeed the very integrity of the legal sys­tem is raised.

If experts are doing due dili­gence in enhanc­ing the qual­ity of their foren­sic work, includ­ing the thor­ough­ness and integrity of their meth­ods and opin­ions, two recent arti­cles, one a major con­tri­bu­tion, address these issues.

First, the arti­cle by Christensen et al (2014), Error and its mean­ing in foren­sic sci­ence. Journal of Forensic Science, 59, 1, 123–126, addresses the fun­da­men­tal ques­tion of error.

What is error? Is error com­mon, inevitable, cor­rectable, or avoid­able? Are you aware that you even have an error rate in your decision-making?

In foren­sic men­tal health assess­ments, research shows that reli­a­bil­ity is poor; hence, height­ened error rates.

What is error? Error means that you made the wrong deci­sion, that your opin­ions are flawed or incor­rect based pro­ce­dural and/or method­olog­i­cal deficiencies…or bias.

What is bias?

A very pow­er­ful arti­cle by Neal & Grisso (2014) pro­vides a con­cep­tual foun­da­tion and call for research on bias in foren­sic men­tal health eval­u­a­tions, address­ing con­scious and uncon­scious biases, includ­ing com­mon cog­ni­tive heuris­tics uti­lized by all human beings, includ­ing sci­en­tists, lawyers, judges, and juries.

They pro­vide clear and con­cise def­i­n­i­tions and con­cep­tual issues for address­ing the con­cep­tual foun­da­tions of bias. This work in rooted in the sem­i­nal, 1974 arti­cle by Tversky & Kahneman, which opened the whole era of cog­ni­tive heuris­tics and the role of bias in the intu­itive judg­ment of prob­a­bil­ity under con­di­tions of uncertainty.

Hard going in the read, but valu­able in the payoff.


Neal, T., & Grisso, T. (2014). The cog­ni­tive under­pin­nings of bias in foren­sic men­tal health eval­u­a­tions. Psychology, Public Policy, and the Law, on line publication.

Tversky, A., & Kahneman, D. (1974). Judgment under uncer­tainty: Heuristics and biases. Science, 185, 27 September 1974, 1124–1131.

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