EP5-A2. ISBN Volume 24 Number ISSN Evaluation of Precision Performance of Quantitative Measurement. Methods; Approved. Evaluation of Precision Performance of Quantitative Measurement Methods; Approved Guideline, EP05A2E. Clinical and Laboratory Standards Institute (CLSI) document EPA2 describes the protocols for determining the precision of a method. The precision of a.
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Within-Laboratory Precision Finally, we can calculate the total or within-laboratory SD s e05 using the equation: For a normal distribution the measure of imprecision is the standard deviation SD.
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You may delete a document from your Alert Profile at any time. Summing the square of the differences gives a total of 0. This standard is also available to be included in Standards Subscriptions. Selection and analytical evaluation of methods with statistical techniques.
CLSI document EPA2 describes the protocols that should be undertaken by the user to verify precision claims by a manufacturer. When using quality control samples, these should be different to those used to ensure the instrument is in control at the time of the assessment.
It is generally assumed in the laboratory that the variation associated with repeated analysis will follow a normal distribution, also known as the Laplace-Gaussian or Gaussian distribution. For the purposes of this discussion reproducibility will not be considered, as it involves multiple laboratories. You should contact the package authors for that. There is some variation in the terminology used but for the purposes of this discussion, repeatability, also known as within-run precision, is defined as the closeness of agreement between results of successive measurements obtained under identical conditions.
Evaluating Assay Precision
The first step is to calculate the mean of the replicates for each day, then for each result subtract the mean for that day and square the resultant value. For more information on customizing the embed code, read Embedding Snippets.
On 20 days two separate runs with two replicates of the same sample dp05 measured.
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Finally, we can calculate the total or within-laboratory SD s l using the equation:. Dr Douglas Chesher e-mail: However, for a method developed in-house a higher level of proof is required to validate the method, in which case EPA2 would be the appropriate guideline to use. Open in a separate window. Repeatability A Value In order to compare the estimated repeatability to a claimed value we can calculate the critical or verification value using the equation: Support Center Support Center.
Journal List Clin Biochem Rev v. CLSI now uses the term within-laboratory precision to denote the total precision within the same facility using the same equipment 1 and this term will be used for this concept throughout this paper. Standards Subscriptions from ANSI provides a money-saving, multi-user solution for accessing standards.
In order to compare the estimated repeatability to a claimed value we can calculate the critical or verification value using the equation:.
The EPA2 protocol is similar except that the experiment is undertaken with three replicates over five days for at least two levels. Note, some authors refer to total variation as just the between-run component instead of combined between-run and within-run shown above. A balance is created in the sp05 between complexity of design and formulae, and simplicity of operation.
Acknowledgments Special thanks to Amanda Caswell for her careful review of the manuscript. Summary When evaluating the precision of a method it is necessary to assess the repeatability within-run ep055 the total or within-laboratory precision.
Instead total precision within a laboratory within-laboratory precision will be assessed. Each level is run in duplicate, with two runs per day over 20 days, and each run separated by a minimum of two hours.
Evaluating Assay Precision
If the repeatability and within-laboratory SD are less than that indicated by the manufacturer, then the user has demonstrated precision consistent w2 the claim and no further calculations are required. Table 2 shows the results of each of these calculations. As the period of assessment is quite short, the total Epp05 or within-laboratory SD derived from these experiments should not generally be used to define acceptability limits for internal quality control. The procedures are designed for manufacturers or developers of clinical laboratory measurement methods, and for users of those methods who wish to determine their own performance capabilities or to verify claims from a manufacturer.
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