1.1 ,This guide covers the evaluation and interpretation of proficiency test program (PTP) results. For proficiency test program participants, this guide describes procedures for assessing participants’, results relative to the collective PT program results and potentially improving the laboratory’,s testing performance based on the assessment of findings and insights. For the committees responsible for the test methods included in PT programs, this guide describes procedures for assessing industry’,s ability to perform test methods and for potentially identifying opportunities for improvements.