Associations between police lethal force errors, measures of diurnal and reactive cortisol, and mental health

Errors in lethal force by police are met with significant demand for explanations as to why they occur, stimulating a growing body of multidisciplinary research. Acutely stressful occupational conditions result in decrements to police performance, including lethal force decision-making. Further, although it is known that repeated and prolonged exposure to potentially traumatic work-related encounters is linked to higher rates of mental health symptoms, it is unclear if psychological symptoms are related to police performance, and lethal force errors specifically. The present study tested the relationships between biological stress and psychological symptoms on lethal force errors among a combined sample of non-clinical, active-duty frontline (n = 57) and tactical (n = 44) police officers. Specifically, biological measures included: diurnal (cortisol awakening response - CAR), and reactive cortisol (prior to and in response to realistic critical incident (CI) simulations). Psychological self-reported symptoms included: pre-CI stress, depression, anxiety, PTSD, and occupational stress. Tactical officers displayed higher CAR compared to frontline officers, consistent with prior research. When including outliers, CAR significantly predicted lethal force decision-making errors; however, the effect does not remain once removing the influence of outlier CAR observations. The current findings suggest that biological measures of reactive cortisol may be too nonspecific to predict lethal force errors during acutely stressful police operations and measures of diurnal cortisol are heavily influenced by outlier values. Non-clinical levels of psychological symptoms (as measured in this study) do not appear to interfere with lethal force decision-making. It remains to be tested if clinically diagnosed disorders would interfere with police performance. Implications for future applied health research are discussed.