Process Capability and Stability of Analytical Systems Assessed from Proficiency Testing Data

valuable adjunct to laboratory activities dedicated to the maintenance of reliable analytical methods. The PT pro-gram may facilitate continuousquality improvement if lab-oratory performance is presented in the context of expec-tations espoused by healthcare professionalsfor optimal patient care. Statistical process control (SPC) and capa-bilityanalysis are tools used by industryin a Total Quality Management environment to characterize and monitor the performance of its processes relative to performance specifications. I conceptualized the use of an analytical system by many laboratories as a process that periodi-cally produces resultsfrom the analysis of PT specimens. I treated a set of five PT results (theophytline)reported by a laboratory as a process sample and subjected the sam-plescollected from many laboratories to SPC and capabilit