CCIL Laboratory Proficiency Testing and Correlation Programs

Question 1

What is the primary purpose of participating in an inter-laboratory proficiency testing (PT) program?

Accepted Answer

To evaluate a laboratory's performance by comparing its test results against those of other participating laboratories using the same reference material

Answer

Proficiency testing programs provide an objective, external measure of a laboratory's measurement performance. Each participant tests an identical or homogeneous material and submits results; the program coordinator statistically compares all results to identify laboratories with systematic bias or poor precision. ISO/IEC 17025 requires accredited laboratories to participate in PT programs relevant to their scope.

Question 2

In a proficiency testing program, what does a Z-score of +3.2 indicate about a laboratory's result?

Accepted Answer

The result is 3.2 standard deviations above the assigned reference value, flagging a potential systematic positive bias

Answer

A Z-score = (x - X) / σ, where x is the laboratory's result, X is the assigned reference value, and σ is the standard deviation of the PT scheme. |Z| ≤ 2 is satisfactory, 2 < |Z| ≤ 3 is a warning (questionable performance), and |Z| > 3 is an action signal indicating statistically significant deviation requiring investigation and corrective action.

Question 3

When a laboratory receives an unsatisfactory Z-score result from a proficiency test, what is the required first step under ISO/IEC 17025?

Accepted Answer

Conduct a root cause investigation and document corrective actions to address the identified deficiency

Answer

ISO/IEC 17025 (clause 7.7 and 8.7) requires that when nonconforming work or unsatisfactory PT results are identified, the laboratory must conduct a root cause analysis to determine why the deviation occurred (e.g., equipment fault, technician error, sample handling issue) and implement corrective actions to prevent recurrence. The investigation and actions must be documented.

Question 4

What is the En (Normalized Error) ratio used for in proficiency testing?

Accepted Answer

To assess laboratory performance when both the laboratory's uncertainty and the reference value uncertainty are known

Answer

The En ratio = (x - X) / √(U²lab + U²ref), where U values are the expanded uncertainties of the laboratory result and the reference value. |En| ≤ 1.0 indicates satisfactory performance. The En ratio is preferred over Z-scores when measurement uncertainty values are available, as it accounts for the uncertainty of both the participant's result and the reference value.

Question 5

In CCIL's correlation testing program for asphalt or concrete laboratories, what is the primary distinction from typical PT programs?

Accepted Answer

Participants test the same physical materials using standardized procedures, focusing on technician proficiency and equipment performance within the CCIL network

Answer

CCIL's correlation (round-robin) testing programs circulate common physical samples (e.g., aggregate, asphalt mixtures, concrete) among member laboratories. The goal is to identify sources of between-laboratory variability, verify that technicians are following standardized CSA/ASTM/AASHTO procedures correctly, and ensure that equipment is properly calibrated and maintained — directly supporting CCIL's inspection and accreditation process.

CCIL - Canadian Council of Independent Laboratories Practice Test

CCIL - Canadian Council of Independent Laboratories Practice Test

CCIL Laboratory Proficiency Testing and Correlation Programs