CLSI EP5 PDF
1- & 2- precision over days, CLSI-EP5. This procedure is available in the Analyse -it Method Evaluation edition. Precision determines the variation of a method. NCCLS document EP5-A2 (ISBN ). NCCLS, West Valley Road, Suite , Wayne, Pennsylvania USA, THE NCCLS . Buy CLSI EP5 A2 Ed. 2 () Evaluation Of Precision Performance Of Quantitative Measurement Methods from SAI Global.
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Total precision within device or laboratory and repeatability within run can be compared against a manufacturer’s claim to demonstrate a method is operating correctly. Linnet K, Boyd JC.
Various materials may be used to complete the assessment with either protocol. While the term precision relates to the concept of variation around a central value, imprecision is actually what is measured. The experiment produces at least 25 replicates collected over at least 5 days for each sample material. Table 2 shows the results of each of these calculations. Please be aware that Analyse-it is only available for Microsoft Windows.
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CLSI EPA3: verification of precision and estimation of bias – Westgard
Use of these materials is important in establishing the traceability of measurement procedures. Calculation of the verification interval eo5 be complicated, but the committee simplified it greatly by providing tables for the difficult-to-calculate quantities based on the number of replicate measurements per run, the number of runs, and the uncertainty of the target value. If an outlier is found the pair should be rejected and the cause investigated and resolved before repeating the run.
The user must evaluate the estimated bias versus allowable bias. Summary When evaluating the precision of a method it is necessary to assess the repeatability within-run and the total or within-laboratory precision.
CLSI EP5 1- & 2- run precision | Analyse-it®
Estimating Precision When evaluating the precision of an assay, the trivial approach for estimating repeatability for any given level is to perform 20 replicate analyses in a single run on a single day. Internationally recognized high order reference materials, such as a material from the U.
This could be useful, for example, if the intent of the experiment was to estimate the bias of one laboratory in a system relative to another, or to the mean of the laboratories in a system.
For this, longer-term assessment is required. A spreadsheet for assisting with the calculations described in this article is available from the AACB web-site.
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. Run the Analyse-it trouble-shooter For customers If the pre-assigned concentration is not known, the mean is used as an estimate of the true concentration. When undertaking the assessment the data must be assessed for outliers, which are considered to be present if the absolute difference between replicates exceeds 5.
In order to compare the estimated repeatability to a claimed value we can calculate the critical or verification value using the equation:. No literary matter in The Clinical Biochemist — Reviews is to be reproduced, stored in a retrieval system or transmitted in any form by electronic or mechanical means, photocopying or recording, without permission. If QC material is being used for the precision assessment, it should be different to that used to control the assay.
Support Center Support Center. Within-Laboratory Precision Finally, we can calculate the total or within-laboratory SD s l using the equation: The powerful statistical analysis you’d expect from an expensive statistics package. Tools, Technologies and Training for Healthcare Laboratories. If the p-value is significant the observed precision is statistically worse than the claim. When entering new data we recommend using New Dataset to create a new precision dataset. Journal List Clin Biochem Rev v.
If a day is excluded due to missing values the observations for that day are not plotted, but if a day is excluded due to outliers determined using the preliminary SD, see below the day’s observations are shown as red crosses. A method measured on a continuous scale over a number of days, with one or two runs per day. 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.
Estimation of Bias Because the precision experiment has so many replicate measurements, collected over several days, results from the precision experiment may be used to make a reliable estimate of the bias of the measurement procedure relative to the assigned target values of the sample materials used in the experiment. For the purposes of this example the results of only a single level are shown Table 1.
Care must be taken in knowing which term is being referred to. 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.
Reproducibility is at the other extreme and refers to the closeness of agreement between results of successive measurements obtained under changed conditions clsj, operators, calibrators, reagents, and laboratory.
However, if the values achieved are greater than those reported by the manufacturer, a statistical test needs to be performed to determine whether this difference is statistically significant. Second, most manufacturers provide only regression statistics as the results of comparison experiments, and do not provide bias claims, cpsi the user has to calculate the bias to be expected from the regression statistics provided and has little idea of the uncertainty of this estimated bias.
There were two problems with this approach. To clsu a preliminary SD: Using the values from our example the mean of all the results is 1.
As alluded to above, EPA2 is generally used to verify that a method is performing as is claimed by the manufacturer. Unfortunately this approach is insufficient, as it tends to under-estimate repeatability, as the operating conditions in effect at the time may not reflect usual operating parameters.
Evaluating Assay Precision
Because the precision experiment has so many replicate measurements, collected over several days, results from the precision experiment may be used to make a reliable estimate of the bias of the measurement procedure relative to the assigned target values of the sample materials used in the experiment.
All backed by our day money-back guarantee. The following example relates to the verification of performance of calcium according to EPA2 using a five day protocol.
For bias relative to the quality control peer group, quality control materials with peer group values for the measurement procedure are appropriate. Each level is run in duplicate, with two runs per day over 20 days, and each run separated by a minimum of two hours.
Click Compare against and select Imprecision specification. Part of the process of verifying or validating a method to confirm that it is suitable for use is an assessment of precision. Click Compare against and select Performance claim.