Analysis of Competing Hypotheses (ACH) — a method for de-biasing forensic decision making

I recently attended a three day workshop on school, campus, and workplace threat assessment and became acquainted with ACH. It is a methodology developed by the CIA and is used to consider evidence when factors are complex or ambiguous. Given the many factors that can influence forensic decision making, including examiner decision thresholds, cost of errors, cognitive heuristics (confirmation bias, availability, and representativeness are the most common), and random error, an ACH matrix is an efficient method for examining data that supports decisions/opinions, through step by step support or refutation of hypotheses. I will be putting together sample ACH matrices for CST, NGRI, and post-acquittal CR and posting them.

Freeware for constructing ACH matrices is available on the web (http://www2.parc.com/istl/projects/ach/ach.html). ACH is widely available and free. When incorporated with procedure checklists for forensic reports, an ACH matrix is likely to strengthen the rigor and quality of forensic opinions.

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