Intermediate precision test

Precision studies can be planned in a full factorial matrix-type format involving multiple analysts, days, capillaries, buffer preparations, instruments, etc. Table 9 displays an example matrix for intermediate precision testing involving two analysts, two instruments, and two capillaries over a multiple day period. Typically, qualification targets for acceptable precision will be pre-defined based on method type, capability, and intent. Acceptable targets can also be mathematically determined by the method of Horwitz. ... 

A single run performed during intermediate precision testing can also be designated in advance for repeatability testing (see run 3 in Table 9), resulting in less total runs. 

If automation is utilized, then an intermediate precision test is required to compare results obtained through manual testing versus automated testing (if all solvent composition and analyte concentrations of all actives are identical in both methods). 

For non-compendial procedures, the performance parameters that should be determined in validation studies include specificity/selectivity, linearity, accuracy, precision (repeatability and intermediate precision), detection limit (DL), quantitation limit (QL), range, ruggedness, and robustness [6]. Other method validation information, such as the stability of analytical sample preparations, degradation/ stress studies, legible reproductions of representative instrumental output, identification and characterization of possible impurities, should be included [7], The parameters that are required to be validated depend on the type of analyses, so therefore different test methods require different validation schemes. 

The validation process begun in Phase I is extended during Phase II. In this phase, selectivity is investigated using various batches of drugs, available impurities, excipients, and samples from stability studies. Accuracy should be determined using at least three levels of concentration, and the intermediate precision and the quantitation limit should be tested. For quality assurance evaluation of the analysis results, control charts can be used, such as the Shewart-charts, the R-charts, or the Cusum-charts. In this phase, the analytical method is refined for routine use. 

Within-laboratory reproducibility/intermediate precision Precision under conditions where independent test results are obtained with the same method on identical test items in the same laboratory by different operators using different equipment on different days. 

Two unique sample tests (e.g., different analysts, instruments, reagents, and standard preparations) performed within the same laboratory would establish the method s intermediate precision. If the dosage form requires the use of a sinker, the sinker specified in the method should be used in precision testing. 

Precision and accuracy Quantitative analysis by NMR is very precise with relative standard deviations for independent measurements usually much lower than 5%. The largest errors in NMR measurements are likely due to sample preparation, not the NMR method itself. If a good set of standards is available and all NMR measurements for the test and standard samples are performed under the same acquisition conditions, the quantitative results can be readily reproduced on different instruments operated by different analysts at different times. Therefore, good intermediate precision can also be achieved. An accurate quantitative NMR assay will require accurately prepared standards. The accuracy of an NMR assay can be assessed, for example, by measuring an independently prepared standard or an accurate reference sample with the assay. In many cases, a spike recovery experiment can also be used to demonstrate the accuracy of an NMR assay. 

Intermediate precision is another measure of the performance of the method where samples are tested and compared using different analysts, different equipment, different days, etc. This study is a measure of interlab variability and is a measure of the precision that can be expected within a laboratory. Intermediate precision is not required if a reproducibility study has been performed. Table 6 lists the ranges and suggested acceptance criteria for evaluation of precision during method development. 

Reproducibility is the third and final portion of precision testing. Here, samples are prepared and compared between testing sites. This usually occurs at the time of technology transfer. Samples are prepared in a similar manner between the two sites and are compared to a previously agreed-upon set of acceptance criteria. As per the ICH, reproducibility studies are not a part of submission filings, but should be performed as a confirmation of the ability of each testing site to perform the method reliably. An executed reproducibility study can be used in place of intermediate precision for the validation of a method, although there is no problem if both validation parameters are evaluated. 

Intermediate precision has been tested by repetitive analysis on five separate days. For each day the electrolyte, sample, and standard solutions should be freshly prepared to include errors from, e.g., weighing and diluting. Variations to be studied also include multiple analysts, multiple equipment, and multiple sets of reagents in the same laboratory. ... 

As an identity (ID) test, per ICH guidelines, only selectivity is required in method qualification and validation. Repeatability and intermediate precision are often included to ensure reliability of p7 determinations. Additionally, method robustness should be tested to assure that the assay performance is suitable for QC environment. Quantitative parameters such as LOD/LOQ are not required for an ID assay. If a cIEF method is used for purity determination, then all the purity parameters shown in Section 4 should be qualified. The following sections illustrate an example of method development and qualification procedures for cIEF. 

Intermediate precision generally incorporates test results from several assays both within a day and day-to-day over a time period (e.g., days, months, etc.). If appropriate, it includes replicates of multiple samples from various analysts and instruments. As in the repeatability studies, intermediate precision is determined by calculating mean, SD, and RSD values across analyst-to-analyst, instrument-to-instrument, and day-to-day studies. Intermediate precision can be reported as an SD or RSD value, depending on preference. 

Depending on the use of the assay, different parameters will have to be measured during the assay validation. Validation of analytical assays is the process of establishing one or more of the following as appropriate to the type of assay accuracy precision (repeatability, intermediate precision), linearity, range, limit of detection, limit of quantification, specificity, and robustness [1]. For physicochemical methods there are accepted defined limits for these test parameters ... 

Control sample a representative batch of drug substance (or drug product). Typically, control samples are tested in all analyses to ensure consistency in method performance across different runs. Sometimes, they are used as part of the system suitability test to establish the run-to-run precision (e.g., intermediate precision, reproducibility). 

Intermediate Precision. Intermediate precision expresses within-laboratory variation and is generally performed on different days using different analysts, equipment, and sample preparations. This test may not be applicable if the laboratory has only one workstation. Additionally, this test may not be appropriate for automated workstations that are operating under the same environment and controls within a laboratory. This assumption is made on the basis that the automated workstations are identical (i.e., same configuration, same software and hardware) and that they have been suitably qualified and maintained to a consistent standard and operate under a similar climatic environment. The influence of the analyst is reduced to the preparation of solvents, and this should be covered by the robustness studies. 

Intermediate precision, defined as the closeness of agreement between individual test results obtained with the same method on identical test material but in one laboratory, where operator and/or equipment and/or time are changed. 

A table of values can be generated using a quasi-simulation from the above formula. (See Table 1.) If one uses the specification of 90.0-110.0% which are frequently used for potency assays of drugs products, and a method intermediate precision (as percentage ofRSD) of2.0 and 2.5%, the values obtained from Table 1 are five and seven samples, respectively. Coincidentally, these values approximate those mentioned in the U.S. v. Barr decision. It should be mentioned that this method of calculating the number of retests may not work well for some tests, such as LAL bioassays, which produce colony counts that are not normally distributed, but skewed. 

The precision has been defined in the ISO 5725-1 standard as the closeness of agreement between independent test results obtained under stipulated conditions [28]. Many factors may contribute to the variability of test results obtained with the same method on identical samples, including (but not limited to) the operators), the equipment, the reagents, the RM(s), the environment, the time between measurements, and the laboratories. The maximal variability of test results is explained by the reproducibility (R) of the method. All factors that have influence on the variability of a test method should be taken into consideration when assessing the reproducibility. The repeatability (r) is assessed by keeping all the above-mentioned factors constant (e.g., same operator, same equipment, same laboratory, short time interval). It is a measure of the minimum variability of a method. The intermediate precision is situated between the two extreme measures of precision repeatability and reproducibility. The terms within-laboratory reproducibility (w), long-term precision, and so on, are often used to demonstrate the intermediate precision of a method. For a correct interpretation of the intermediate precision, the factors that have been taken into account should be known. 

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