Formulae for consistent biometric score level fusion

In an operational setting of key practical importance for a biometric application deployment is the ability to set thresholds to meet error rate targets. Consequently there is a need to consider how output scores from multi-modal score-level fusion are defined. We show a method to ensure these fused scores are consistent with a known input score definition. We derive fusion formulae for the case of input scores based on false acceptance rates. We provide examples to highlight implementation issues.