ISTA quality assurance programme – The proficiency test rating system

Abstract

A rating system for determining a laboratory's performance in the International Seed Testing Association (ISTA) Proficiency Test Programme was developed. The proficiency test programme is run 3 times a year with germination testing, purity testing and other seed determination as major test methods. Each test method is given an A, B, C or below minimum performance (BMP) rating for each test round. A calculation of Z-scores is applied for germination and purity testing ,and the in-round rating is determined based on the number of out-of-tolerance results (±2.0) and the sum of absolute Z-scores. In-round rating for determination of other seeds is based on the percentage of retrieved seeds. The in-round rating is accumulated over six test rounds to determine the laboratory's overall testing performance. Laboratories showing a poor overall performance are suspended from accreditation until proof can be given that performance has improved.