Score averaging for alien species risk assessment: a probabilistic alternative

Area of Science:

• Ecology
• Risk Assessment
• Biosecurity

Background:

• Ordinal scoring systems are common in biological risk assessment, particularly for invasive alien species and quarantine pests.
• Current methods often disaggregate risk into components, scoring each and then averaging to determine overall risk.
• Score-averaging lacks a satisfactory theoretical basis and can be suboptimal for risk quantification.

Purpose of the Study:

• To develop a more robust method for calculating overall risk from component scores in biological risk assessments.
• To improve the discrimination between high and low-risk scenarios compared to existing methods.
• To provide a more reliable measure of risk that aligns better with expert judgment.

Main Methods:

• Proposed a novel approach using linear mapping of ordinal scores to notional probabilities.
• Utilized conditional probability principles to derive an overall risk measure from component probabilities.
• Compared the efficacy of this new method against traditional score-averaging techniques.

Main Results:

• The linear mapping and conditional probability approach demonstrated improved discrimination between high and low-risk cases.
• Results showed closer correspondence with independent expert judgment than score-averaging.
• The new method offers a more nuanced and accurate quantification of biological risks.

Conclusions:

• The proposed method of mapping scores to probabilities provides a superior alternative to score-averaging for biological risk assessment.
• This approach enhances the reliability and accuracy of risk quantification for invasive species and quarantine pests.
• Further application of this probabilistic method is recommended for improved biosecurity decision-making.