A proposed method using t-test for stability check in proficiency testing in tensile and hardness tests

Proficiency testing is a very powerful tool for laboratories to continuously monitor the validity of the results, and is considered one of the technical requirements for accreditation according to ISO 17025. Stability check for the test samples or artefacts is important to ensure that these samples are fit for purpose, and give consistent performance over a specified period of time. The aim of this work is to propose a method for stability check using t-test as an alternative method of that followed in ISO 13528. The proposed t-test method is applied on proficiency test for Rockwell hardness test, Brinell hardness test, and tensile test for both PVC (Polyvinyl Chloride), and steel reinforcement bars. The results of stability check are analyzed, and compared with the results obtained from the convenient method of ISO 13528. The proposed method excelled the convenient method followed by ISO 13528.  The main advantage of the proposed method using the t-test is that it is independent of the participants’ results; it depends only on the results from the lab, which performs the stability check