[Evaluation of proficiency test with low number of participants:a case study on the testing of lead and nitrite in water].

Objective: The gross error of the assigned value-classical statistical method was developed that all participants in proficiency testing activities could obtain unbiased evaluation in case of a low number of participants(& lt; 17).

Methods: This developed method was employed to evaluate the testing result of nitrite-N and lead in water from participants along the "Belt and Road", which was organized by CNCA in 2019.

Results: Use the specified value gross error-classical statistical method to evaluate the feedback result of 29(15+14) participants with non-normal distribution, 4 out of 15 participants in "Lead in Water" get a "unsatisfied", 5 out of the 14 participants in "Nitrite in Water(as Nitrogen)"get a "unsatisfactory".