1. Introduction

The principle of validation of quantitative analytical procedures is widely spread today in all domains of activities where measures are made. The objective of validation of an analytical method is to demonstrate that the method is suitable for the intended use, such as evaluation of a known product for potency, and impurities. The intent of method validation is to provide scientific evidence that the analytical method is reliable and consistent before it can be used in routine analysis of product. The analytical method validation is governed by the International Conference on Harmonization (ICH).

The key criteria for evaluation of an analytical method are: specificity, accuracy, precision, detection limit, quantitation limit, sensitivity, working range and linearity, robustness and recovery. The ICH definitions for validation characteristics are indexed in Table 1.

The type of method and analytical technique used will determine the nature and extent of the validation studies required. The most common methods for validation are identification, assay and impurities determination (Chapter. 2). Results for each applicable validation characteristic are compared against the selected acceptance criteria.

Besides ICH, other guidance can be referred for detailed information on the international requirements such as the US Food and Drug Administration guidance (FDA) and the United States Pharmacopoeia (USP).

The aim of this work is to furnish a conspectus of regulatory expectations related to statistical analysis and the survey of mutual statistical techniques used to analyze analytical method validation data with some examples.

The following two points are given:

  • Statistics to analyze data for analytical method validation such as mean, standard deviation, confidence intervals, and linear regression.
  • Regulatory guidelines regarding statistical data analysis in analytical method validation.


Table 1 Performance criteria for analytical method validation.

Validation characteristics ICH definitions
Specificity Specificity is the ability to assess unequivocally the analyte in the presence of components which may be expected to be present. Typically these might include impurities, degradants, matrix, etc.
Accuracy The accuracy of an analytical procedure expresses the closeness of agreement between the value that is accepted either as a conventional true value or an accepted reference value and the value found. This is sometimes termed trueness.
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 homogenous sample under the prescribed conditions. Precision may be considered at three levels: repeatability, intermediate precision, and reproducibility.
Repeatability Repeatability expresses the precision under the same operating conditions over a short interval of time. Repeatability is also termed intra-assay precision.
Intermediate precision Intermediate precision expresses within-laboratories variations: different days, different analysts, different equipments, etc.
Reproducibility Reproducibility expresses the precision between laboratories (collaborative studies usually applied to standardization of methodology).
Detection limit The detection limit of an individual analytical procedure is the lowest amount of analyte in a sample that can be detected but not necessarily quantitated as an exact value.
Quantitation limit The quantitation limit of an individual analytical procedure is the lowest amount of analyte in a sample that can be quantitatively determined with suitable precision and accuracy. The quantitation limit is a parameter of quantitative assays for low levels of compounds in sample matrices and is used particularly for the determination of impurities and/or degradation products.
Linearity The linearity of an analytical procedure is its ability (within a given range) to obtain test results that are directly proportional to the concentration (amount) of analyte in the sample.
Range The range of an analytical procedure is the interval between the upper and lower concentration (amounts) of analyte in the sample (including these concentrations) for which it has been demonstrated that the analytical procedure has a suitable level of precision, accuracy, and linearity.
Robustness The robustness of an analytical procedure is a measure of its capacity to remain unaffected by small, but deliberate, variations in method parameters and also provides an indication of its reliability during normal usage.

Table 2 Validation characteristics according to the nature of the test.

Type of analytical procedure characteristics Identification Testing for impurities Assay dissolution
(measurement only)
Content/potency
    Quantitative Limit  
Accuracy – + – +
Precision        
Repeatability – + – +
Intermediate precision – + (1) – + (1)
Specificity (2) + + + +
Detection limit – − (3) + –
Quantitation limit – + – –
Linearity – + – +
Range – + – +
Robustness – + – +