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. 2018 Oct;60(10):867-874.
doi: 10.1097/JOM.0000000000001401.

Reducing Lethal Force Errors by Modulating Police Physiology

Free PMC article

Reducing Lethal Force Errors by Modulating Police Physiology

Judith Pizarro Andersen et al. J Occup Environ Med. .
Free PMC article


Objectives: The aim of this study was to test an intervention modifying officer physiology to reduce lethal force errors and improve health.

Methods: A longitudinal, within-subjects intervention study was conducted with urban front-line police officers (n = 57). The physiological intervention applied an empirically validated method of enhancing parasympathetic engagement (ie, heart rate variability biofeedback) during stressful training that required lethal force decision-making.

Results: Significant post-intervention reductions in lethal force errors, and in the extent and duration of autonomic arousal, were maintained across 12 months. Results at 18 months begin to return to pre-intervention levels.

Conclusion: We provide objective evidence for a physiologically focused intervention in reducing errors in lethal force decision-making, improving health and safety for both police and the public. Results provide a timeline of skill retention, suggesting annual retraining to maintain health and safety gains.

Conflict of interest statement

Andersen, Di Nota, Beston, Boychuk, Gustafsberg, Poplawski, and Arpaia have no relationships/conditions/circumstances that present potential conflict of interest.


Lethal force error rates during critical incident scenarios before and after the physiological intervention. Performance (ie, correct shoot/no shoot decisions) was scored by expert Use of Force Instructors, and showed a 67% decrease in errors of lethal use of force following the physiological intervention (nine errors pre-intervention, three errors post-intervention of 171 opportunities), which was maintained at 6-month (1 error of 117 opportunities, 84% reduction) and 12-month (1 error of 84 opportunities, 77% reduction) evaluations. Gains in police performance began to reverse at 18-month retention evaluation (3 errors of 87 opportunities, 35% reduction relative to pre-intervention error rates). Retention of the participant sample was maintained throughout the study, with 81% of officers (46/57) returning for at least one follow-up evaluation conducted at 6, 12, and 18 months.
Indices of autonomic arousal during stressful critical incident scenarios. Relative to their individual resting baseline HR, officers’ maximum heart rate (HR_Max) increased significantly from pre- to post-intervention (P = 0.002). HR_Max at 12 months was significantly lower than all previous time points, but plateaued during scenarios evaluated at 18-month retention [F(4, 57) = 8.894, P = 0.000]. Error bars show standard error of the mean.
Autonomic recovery time following stressful critical incident scenarios. Recovery time (in seconds) from HR_Max during critical incident scenarios to average resting baseline was significantly faster at 12-month follow-up relative to pre-intervention (P = 0.042), post-intervention (P = 0.009), and 6-month evaluations (P = 0.004). Recovery time was also faster at 18-month follow-up relative to post-intervention (P = 0.019) and 6-month evaluations (P = 0.030), but plateaued after 12-month follow-up [P = 0.177) (F(4, 61) = 5.094, P = 0.001]. The variability (shown by error bars) in recovery time also decreased over time, demonstrating that the intervention was effective in reducing the number of outliers with extremely high or low recovery times. Error bars show standard error of the mean.
Mapping autonomic arousal and lethal use of force decision-making errors. When considered together, increased autonomic arousal at post-intervention and 6-month retention intervals (hatched bars) coupled with reduced lethal force errors (black bars) suggest improved modulation of autonomic arousal that is matched to the demands of threatening and occupationally relevant scenarios. With continued practice, autonomic arousal modulation and resultant improvements in police use of force decision-making (reflected by reduced error rates) are sustained at 12 and 18 months, supporting the efficacy of the current intervention.

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