A framework for evaluating the frequency of external quality assessment challenges

Abstract

Background and aims: No clear rules about the optimal frequency of organizing External Quality Assessment (EQA) rounds exist. More frequent challenges will facilitate faster responses and more reliable statistics. Adding extra samples leads to extra information, but the correlation between results from different samples reduces the extra information from additional samples.

Materials and methods: Data were used for ALT and Albumin from the RCPAQAP EQA scheme. Every two weeks, laboratories analysed two samples. Correlation between results of different samples was calculated to determine the power of distinguishing poorly from well-performing laboratories. The power was compared to hypothetical cases of no correlation and one-sample-per-week to estimate the number of samples negated due to correlation.

Results: Correlation leads to negation of a number of samples, but not more than 50% of samples were negated. The number of negated samples was positively related with the correlation between EQA results.

Conclusions: The proposed framework provides a quantitative evaluation of the impact of adding more EQA rounds or samples. A correlation exists and is higher for analyses performed closer in time, but the examples shown here did not show a detrimental effect on correctly evaluating laboratories.

Keywords: ALT; Albumin; Correlation; External quality assessment.