Effect of Favourable Treatment of Samples on Indices of Performance in External Quality Assessment Schemes

Abstract

This study was carried out to examine the effect on performance, as assessed by external quality assessment schemes, of ( a) replicate analysis of external quality assessment samples, and positioning of external quality assessment samples immediately after the calibrants, and ( b) alteration of results on the basis of previous performance in order to bring them closer to the method mean values obtained from all laboratories participating in the external quality assessment scheme. Indices of performance were then compared with those obtained from our normal practice where external quality assessment samples were treated as patient samples. Using these methods we were unable to improve significantly our precision or league ranking based on precision over the six-month period of study. We were able to reduce our bias from method means but at the expense of making precision and league ranking worse.