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commercial analyst concentrations, without concern for covering a wide range of analyte
concentrations. So in practice, we find that PT data have a more limited range than would a
designed CS data set.
In the past, the purpose of proficiency tests was to verify the correct implementation of a method
in a laboratory. As a part of laboratory accreditation, the laboratory must demonstrate
proficiency vs. other laboratories or against traceable standards or reference materials. Similarly,
Method Validation was a process used prior to implementation to assure the method could be
used in more than one laboratory and be shown to have a reasonable level of laboratory
reproducibility. ISO 5725 is the standard used to design validation experiments and to analyze
the results of multi-lab validation studies. Table 1 is a summary of the traditional differences
between the Validation process and Verification.
Method Development
Method Validation
Method Verification
Table 1
Validation
Verification
After Method Development
After Validation
Pertains to the Method
Pertains to the Laboratory
Validation can be
Single Laboratory
Multiple Laboratory
Generally requires multiple laboratories, but
can be done as a single laboratory with a
certified RM
ISO 5725
ISO 13528
Validation Experiments/
Collaborative Studies
Verification Experiments/
Proficiency Tests (PT)
Strict Control of Method
Loose method control
Statistical Output
Reproducibility
Repeatability
Trueness or Bias
Statistical Output:
z-score for each lab
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