Jump to Levey-Jennings Charts - This procedure generates Levey-Jennings control charts on single variables. It finds out-of-control points using. ![]() This lesson discusses one of the cornerstones of QC practice. Avid pro tools 10 torrent. We can no longer take for granted that everyone knows how to build a control chart, plot the control values, and interpret those results correctly. Barry, co-author of Cost-Effective Quality Control: Managing the Quality and Productivity of Analytical Processes, provides a primer on how to construct, use, and interpret the Levey-Jennings chart. • • • • • • • Please Note: This article is from the first edition. An updated version is now available in You can link here to an online calculator which will calculate control limits for you. This exercise is intended to show, in step-wise fashion, how to construct a Levey-Jennings control chart, plot control values, and interpret those results. This assumes you already have (a) selected appropriate control materials, (b) analyzed those materials to characterize method performance by collecting a minimum of 20 measurements over at least 10 days, (c) calculated the mean and standard deviation of those data, and (d) selected the number of control measurements to be used per run and (e) selected the control rules to be applied. See for more information about selecting appropriate control materials. See for detailed information about calculating the mean and standard deviation. See for a description of the approach, tools, and technology available to select QC procedures on the basis of the quality required for a test and the performance observed for a method. Example application For a cholesterol method, two different commercial control products have been selected that have concentrations near the important medical decision levels of 200 mg/dL and 240 mg/dL identified by the National Cholesterol Education Program (NCEP) guidelines for test interpretation. The materials were analyzed once per day for a period of twenty days. From these data, the means and standard deviations were calculated to be: Control 1 Mean=200 smeas= 4.0 mg/dL, or 2.0% CV Control 2 Mean=250 smeas= 5.0 mg/dL, or 2.0% CV QC procedure(s) to be implemented Each of the two control materials will be analyzed once per run, providing a total of two control measurements per run. Control status will be judged by either the 1 2s or 1 3s rule. These rules are defined as follows: • 1 2s refers to the control rule that is commonly used with a Levey-Jennings chart when the control limits are set as the mean plus/minus 2s. In many laboratories, this rule is used to reject a run when a single control measurement exceeds a 2s control limit. • 1 3s corresponds to a Levey-Jennings chart having control limits set as the mean plus/minus 3s. An analytical run is rejected when a single control measurement exceeds a 3s control limit. The 1 2s rule is very commonly used today, and while it provides high error detection, the use of 2s control limits gives an expected high level of false rejections. The 1 3s rule provides an alternative QC procedure that has lower false rejections, but also lower error detection. In this exercise, you will see how to apply both QC procedures and also get a feel for the difference in their performance. Calculation of control limits Two sets of control limits will be needed to implement the rules described above. The first set uses 2s control limits (for implementation of the 1 2s rule) calculated as the mean plus or minus 2 times the standard deviation. The second set uses 3s control limits (for implementation of the 1 3s rule) calculated as the mean plus or minus 3 times the standard deviation. For this example, Control 1 has a mean of 200 and a standard deviation of 4 mg/dL. The upper control limit would be: 200 + 2*4, which is 208 mg/dL. The lower control limit would be: 200 - 2*4, or 192 mg/dL. • What are the 3s control limits for Control 1?
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