AccuReg: Understanding Analytical Validation Parameters

The Regulatory Clinic - July 1996
Understanding Analytical Validation Parameters

Dear Clinic:

Our validation team recently met to define and apply a number of new terms: Ruggedness, reproducibility, intermediate precision, and repeatability. Although we consulted several references, we could not reach a consensus on the intended meanings of these terms as they apply to analytical validations. Can you explain these terms and their significance? Are there any definitive references available?

Divided and Unvalidated, Akron, Ohio

Dear D&U:

Having gone through a similar exercise last year, we certainly can empathize! However, the good news is that we survived, and eventually, concurred. We'll be happy to provide you with our consensus regarding these terms, but first let us offer some background information to explain how we reached agreement.

Since you indicated that you consulted several references during your research, you probably are aware that several publications were issued in 1995 that addressed the issue of analytical method validation. Each of these publications included new definitions of analytical parameters, including those you mentioned in your letter. The three publications we consulted were:

Federal Register, Vol. 60 No. 40, Wednesday March 1, 1995, Docket No. 94D-0016. Final Guideline, "Text on Validation of Analytical Procedures"
"Reviewer Guidance, Validation of Chromatographic Methods," prepared by the Analytical Methods Technical Committee of the Chemistry, Manufacturing Controls Coordinating Committee of CDER at FDA, November 1, 1994
USP XXIII, General Chapter <1225>, "Validation of Compendial Methods," January 1, 1995

Each of these documents contains specific descriptions of FDA's expectations in the area of method validation, but offers slightly different interpretations of certain parameters. Specifically, the most problematic discrepancies in interpretation are found in definitions for the three new parameters of precision (repeatability, intermediate precision and reproducibility), and the modified parameter of ruggedness. All four of these parameters provide for a measure of the variability of the method; a determination as to which parameters are appropriate for your method depends on the method's intended use, as well as on the size of your staff and capabilities of your facility.

As a first step, we determined that the definitions of these parameters apply to the method as performed in its entirety, i.e., the procedure, equipment, environment, analysts, materials, calculations--essentially everything that can influence the results of the analysis.

We then determined that repeatability and intermediate precision apply to intra-laboratory (within laboratory) variability, and that reproducibility and ruggedness apply to inter-laboratory (between laboratories) variability. In fact, we further agreed that the two inter-laboratory parameters are the same measurements. However, defining the relationships that would be considered inter-laboratory proved to be less simple. For both the reproducibility and ruggedness definitions, "between laboratories" may apply to R&D vs. QC; QC 1 vs. QC 2; Location A vs. Location B; vendor vs. client, etc.

Once these concepts were addressed, we were able to develop "generic" definitions that would be applicable to our diverse clientele, ranging from tightly-staffed biotech start-up firms and small OTC manufacturers, to corporate pharmaceutical and biologics operations housing R&D, tech transfer, and multiple-laboratory environments. (As is evident from the discussion of inter-laboratory relationships above, the availability - or lack - of a multiple-laboratory environment plays an important role in the interpretation of reproducibility and ruggedness parameters.)

With that background in place, following are our consensual interpretations of the terms in question:

Precision: The precision of an analytical procedure expresses the closeness of agreement (degree of scatter) between a series of measurements obtained from multiple sampling of the same homogeneous sample under prescribed conditions, and is usually expressed as the variance, standard deviation or coefficient of variation (a.k.a. Relative Standard Deviation) of those measurements. Precision may be considered at three levels: Repeatability, intermediate precision, and reproducibility.
Method Repeatability: The inherent variability of a method which is observed when replicate aliquots of the same homogeneous sample preparation are assayed by a single operator, on the same day, using the same reagents, and the same equipment. (Method repeatability is also known as Intra-assay Variability.)
Method Intermediate Precision: The inherent variability of a method which is observed when subjected to typical operational variables found within the laboratory. Such variables include different analysts, different reagents, and different dates of testing. Method intermediate precision is measured when aliquots from the same homogeneous source sample are separately prepared and assayed by different analysts on different days using different reagents (i.e., separate working samples are prepared), but are tested using the same equipment.
Method Reproducibility/Ruggedness: The inherent variability of a method which is observed when utilized in different laboratories, and hence, different analysts, reagents, equipment, etc. (Method repeatability is also known as Inter-laboratory Variability.)

For more information on analytical assay validations, see the Special Report entitled, "Validation of Analytical Assays and Test Methods for the Pharmaceutical Laboratory" in the Articles section of this month's Regulatory Forum).

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