Base Rate Information Improves Risk Estimation of Laypeople and Experts

Area of Science:

• Forensic Psychology
• Risk Assessment
• Decision Making

Background:

• Psychological assessment interpretation varies by risk level and format.
• Decision makers' probability judgments frequently exceed empirical recidivism rates.
• Previous research has overlooked the impact of base rate information on risk estimation.

Purpose of the Study:

• To investigate the effect of base rate information on risk estimation in laypeople and expert witnesses.
• To determine if base rates reduce the discrepancy between estimated and empirical recidivism rates.
• To explore factors influencing risk assessment accuracy among experts.

Main Methods:

• Two studies were conducted involving laypeople (n=283) and expert witnesses (n=62).
• Participants estimated recidivism risk, with some receiving base rate information.
• Statistical analyses examined the impact of base rates, risk level, and communication format on estimates.

Main Results:

• Both laypeople and experts provided risk estimates significantly higher than empirical base rates (10%).
• Providing base rates reduced the discrepancy between estimated and empirical rates by 12% for laypeople and 7% for experts.
• Experts specializing in risk assessment were more accurate; increased experience correlated with larger discrepancies.

Conclusions:

• Base rate information is crucial for anchoring risk judgments to empirically established benchmarks.
• Communication format had minimal impact, while base rates substantially reduced estimation discrepancies.
• Reporting empirically grounded base rates is recommended alongside any communication format for accurate risk assessment.