4.4.1.4 The proficiency testing provider shall have access to the necessary technical expertise and
experience in the relevant field of testing, calibration, sampling or inspection, as well as statistics. This may be
achieved, if necessary, by establishing an advisory group (named as appropriate).
4.4.1.5 Technical expertise shall be used, as appropriate, to determine matters such as the following:
a) planning requirements as listed in 4.4.1.3;
b) identification and resolution of any difficulties expected in the preparation and maintenance of
homogeneous proficiency test items, or in the provision of a stable assigned value for a proficiency test
item;
c) preparation of detailed instructions for participants;
d) comments on any technical difficulties or other remarks raised by participants in previous proficiency
testing rounds;
e) provision of advice in evaluating the performance of participants;
f) comments on the results and performance of participants as a whole and, where appropriate, groups of
participants or individual participants;
g) provision of advice for participants (within limits of confidentiality), either individually or within the report;
h) responding to feedback from participants; and
i) planning or participating in technical meetings with participants.
4.4.2 Preparation of proficiency test items
4.4.2.1 The proficiency testing provider shall establish and implement procedures to ensure that
proficiency test items are prepared in accordance with the plan described in 4.4.1.
NOTE It is advisable that the proficiency testing provider give due consideration to the preparation of sufficient
numbers of proficiency test items, in order to allow for the need to replace any such proficiency test items lost or damaged
during distribution, or intended to be provided for use after the results of the proficiency testing scheme have been
evaluated. Such uses can include training aids for participants or use as a reference material.
4.4.2.2 The proficiency testing provider shall establish and implement procedures to ensure appropriate
acquisition, collection, preparation, handling, storage and, where required, disposal of all proficiency test items.
The procedures shall ensure that materials used to manufacture proficiency test items are obtained in
accordance with relevant regulatory and ethical requirements.
4.4.2.3 Proficiency test items should match in terms of matrix, measurands and concentrations, as
closely as practicable, the type of items or materials encountered in routine testing or calibration.
4.4.2.4 In proficiency testing schemes that require participants to prepare or manipulate, or both prepare
and manipulate, the proficiency test item and submit it to the proficiency testing provider, the proficiency
testing provider shall issue instructions for preparation, packaging and transport of the proficiency test item.
4.4.3 Homogeneity and stability
4.4.3.1 Criteria for suitable homogeneity and stability shall be established and shall be based on the
effect that inhomogeneity and instability will have on the evaluation of the participants' performance.
NOTE 1 The requirements in this subclause are intended to ensure that every participant receives comparable
proficiency test items, and that these proficiency test items remain stable throughout the proficiency testing. Careful
planning, manufacture and shipping are necessary to achieve this, and testing is usually needed to confirm it.
NOTE 2 In some cases, it is not feasible for proficiency test items to be subjected to homogeneity and stability testing.
Such cases would include, for example, when limited material is available to prepare proficiency testing items.
NOTE 3 In some cases, materials that are not sufficiently homogeneous or stable are the best available; in such cases,
they can still be useful as proficiency test items, provided that the uncertainties of the assigned values or the evaluation of
results take due account of this (see B.3.1.3 and ISO 13528:2005, Annex B).
NOTE 4 Considerations for homogeneity and stability are further discussed in ISO Guide 34, ISO Guide 35 and
ISO 13528.
4.4.3.2 The procedures for the assessment of homogeneity and stability shall be documented and
conducted, where applicable, in accordance with appropriate statistical designs. Where possible, the
proficiency testing provider shall use a statistically random selection of a representative number of proficiency
test items from the whole batch of test material in order to assess the homogeneity of the material.
NOTE In some cases, the use of a random stratified or systematic selection of proficiency test items from the whole
batch is more appropriate.