This document specifies the methodology to determine if a laboratory is in control in the execution of a standard test method. By using statistical control charts and following this document the 'in-statistical-control' status is established and validated. In-statistical-control means the test results produced by the lab on control samples are reasonably consistent with expectation over time; with random variation scattered around a stable expected centre due to common causes only.
This document explicitly defines ‘site precision’ conditions as single apparatus, multi-operators, over a long time horizon. It specifies control charts that are most appropriate for ISO TC28 test methods where the dominant common cause variation is associated with the long term, multiple operator conditions as described by "site precision" conditions. The control charts specified for determination of in-statistical-control are: Individual (I), Moving Range of 2 (MR2), Exponentially Weighted Moving Average (EWMA), and zone-based run rules (commonly known as Western Electric (WE)run rules.
The procedures in this document have been designed specifically for petroleum and petroleum related products, which are normally considered as homogeneous and for test methods which show normality in obtaining their results. However, the procedures described in this document can also be applied to other types of homogeneous products and test methods.