This International Standard complements ISO Guide 43 (all parts) by providing detailed descriptions of sound statistical methods for organizers to use to analyse the data obtained from proficiency testing schemes, and by giving recommendations on their use in practice by participants in such schemes and by accreditation bodies. This International Standard can be applied to demonstrate that the measurement results obtained by laboratories do not exhibit evidence of an unacceptable level of bias. It is applicable to quantitative data but not to qualitative data.