Violence risk assessment and risk communication: The effects of using actual cases, providing instruction, and employing probability versus frequency formats.

TLDR

The study aims to identify factors affecting the validity of violence risk assessment and risk communication for policymakers and practitioners. Researchers presented forensic clinicians with case summaries of mentally ill patients and asked them to estimate the probability of harm within six months and to rate risk level as high, medium, or low. The experiments replicated Slovic and Monahan’s response‑scale effects, showing that more discriminable scales reduced probability estimates, that frequency formats lowered mean likelihoods but heightened perceived risk, and that clinicians’ risk judgments were more influenced by frequency representations than by probability or instruction.

Abstract

This article describes studies designed to inform policy makers and practitioners about factors influencing the validity of violence risk assessment and risk communication. Forensic psychologists and psychiatrists were shown case summaries of patients hospitalized with mental disorder and were asked to judge the likelihood that the patient would harm someone within six months after discharge from the hospital. They also judged whether the patient posed a high risk, medium risk, or low risk of harming someone after discharge. Studies 1 and 2 replicated, with real case summaries as stimuli, the response-scale effects found by Slovic and Monahan (1995). Providing clinicians with response scales allowing more discriminability among smaller probabilities led patients to be judged as posing lower probabilities of committing harmful acts. This format effect was not eliminated by having clinicians judge relative frequencies rather than probabilities or by providing them with instruction in how to make these types of judgments. In addition, frequency scales led to lower mean likelihood judgments than did probability scales, but, at any given level of likelihood, a patient was judged as posing higher risk if that likelihood was derived from a frequency scale (e.g., 10 out of 100) than if it was derived from a probability scale (e.g., 10%). Similarly, communicating a patient's dangerousness as a relative frequency (e.g., 2 out of 10) led to much higher perceived risk than did communicating a comparable probability (e.g., 20%). The different reactions to probability and frequency formats appear to be attributable to the more frightening images evoked by frequencies. Implications for risk assessment and risk communication are discussed.