Monitoring performance of nucleic acid-based diagnostic measurement system users by EQA

External quality assurance (EQA) programmes allow a laboratory to monitor independently its performance and provide feedback to identify and investigate potential areas of concern. However, both the definition of appropriate ‘performance indicators’ and their statistical analysis vary across EQA providers. Typically, performance scores have an unknown statistical distribution and hence arbitrary thresholds are used to measure performance. In this paper, we introduce a scoring system based on well-known statistical principles. The system is simple, flexible and easy to interpret. It can be used to measure performance for single samples or across a panel so providing useful and meaningful information to participants in EQA programmes. The score is illustrated using the 2005 QCMD Hepatitis B Virus Proficiency programme.