Is accreditation useful for quality improvement?

 The Laboratory of the Government Chemist (UK) and the Institute for Reference Measurements and Materials (Belgium) evaluated the correlation between accreditation and performance in proficiency tests. It was concluded that accreditation does not have the expected positive effect on the quality of laboratory results. In this journal discussions conducted on this subject during the CITAC workshop at Pittcon in 1998, were published. No satisfactory explanation for this phenomenon was put forward. In this article, it is proposed that the main effect of accreditation is a decrease of intralaboratory spread. The effect on the trueness of laboratory results is not significant due to the lack of certified reference materials and the low frequency of participation in proficiency tests. Proficiency tests cannot be used to find a correlation between accreditation status and quality without changing the set-up of the proficiency test.