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Whatcom County review finds PSA over‑predicts risk, shows weak accuracy for some outcomes
Summary
A prospective validation of the Public Safety Assessment (PSA) in Whatcom County (Jan. 2019–Mar. 2025, 3,551 defendants) found moderate accuracy for failure‑to‑appear predictions but weaker accuracy and evidence of group bias for new criminal actions and violent outcomes; the analyst recommended recalibration and redesign of the decision matrix.
Whatcom County’s pretrial processes work group heard on Monday that the Public Safety Assessment (PSA) used by the superior court is over‑predicting risk for the county’s pretrial population and shows limited accuracy for some outcomes.
"We find is weak to moderate predictive discrimination," said Dr. Zach Hamilton, a professor of criminology and criminal justice, summarizing his prospective evaluation of 3,551 defendants assessed with the PSA between January 2019 and March 2025. Hamilton said the evaluation paired local PSA scores with outcome data from the Washington State Administrative Office of the Courts (AOC) and looked at three outcomes: failure to appear (FTA), new criminal action (NCA) and new violent criminal action (NBCA).
Hamilton reported an overall AUC (area under the curve) for FTAs of about 0.68, which he described as "moderate" and above commonly cited acceptability thresholds. But he…
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