Analysis of interlaboratory comparisons affected by correlations of the reference standards and drift of the travelling standards

The paper describes a method for analysing interlaboratory comparison results among accredited laboratories. Interlaboratory comparisons are used in order to achieve or to maintain the accreditation following the ISO/IEC 17025 standard. The used approach permits an evaluation of the reference value and of the degree of equivalence in the cases in which the laboratories participating are mutually dependent and the travelling standards are not stable during the comparison. This approach, as an example, was applied to analyse the SIT (Servizio di Taratura in Italia) interlaboratory comparisons carried out for the pressure quantity in the range from 10 MPa to 100 MPa (gage mode and liquid medium) and in the range from 0.15 MPa to 7 MPa (gage mode and gas medium).

► Analysis of interlaboratory comparison results. ► Evaluation of the reference value and of the degree of equivalence. ► Correlations between the measurements of the laboratories. ► Evaluation of the instability of the travelling standards.