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Levey-Jennings Chart Help

A Levey-Jennings chart is often used by laboratories to determine if a certain test method is stable. A control is run on a regular basis (daily, once per shift, etc). The test result from running the control is plotted on the y-axis. The control number (or date) is plotted on the x-axis. Most the time, you will not see a moving range with a Levey-Jennings chart. However, this software gives you the option to include the moving range (with a moving range of two).

The Levey-Jennings chart is very similar to the individuals control chart. The difference is in how the control limits are calculated and the tests used to determine if the process is out of control. The Levey-Jennings chart uses the long-term estimate of the population standard deviation to set the three sigma limits. This is simply the standard deviation calculated using all the data. The individuals control chart uses the estimated standard deviation from the moving range chart. This is the short-term variation based on the within subgroup variation.

The Levey-Jennings chart does not use the basic tests for out of control points that apply to the individuals control chart. Instead, the Westgard rules are applied. These are described below. It should be noted that a moving range chart is not used with a Levey-Jennings chart.

The data used below to demonstrate how to make a Levey-Jennings can be downloaded at this link. This page contains the following:

Data Entry

A lab runs a cholesterol test. To monitor the test, they run a control daily. The control value is 250 mg/dL. They have data for 30 days. The data are entered into a worksheet as shown below. The data can be anywhere on the worksheet and can be in columns (sample identifiers in one column) or in rows (sample identifiers in one row). In the example workbook, the data starts in cell A11.

Creating a New Levey-Jennings Chart

Selecting OK at this point will generate the Levey-Jennings chart. No other entries are required.

The options are:

Note: this example plotted the average of the sample results.  If the control value is known (in this example, the control value is 250), it can be used in place of the average.  This is done with the option “Manual Control Limits” (see below).  With this option, the average can be manually set to 250.

Options for the Levey-Jennings chart

On the input screen for the chart, there is a button labeled “Show Options”.  If you select that button, the input screen will show the options available for the chart.  It is not required to select any of these options.

The options are explained below.

Out of Control Tests

If you select this option, the input screen below is shown.

The out of control tests for the Levey-Jennings chart are known as the Westgard rules.  They are as follows:

Control Limit Options

If you select this option, the input screen below is shown.

The options include:

Titles and Formats

If you select the “Title and Formats” button, the following screen is displayed:

The options include:

Manual Control Limits

If you select the “Manual Control Limits” button, the following screen is displayed:

The options include:

Chart Location

If you select the “Chart Location” button, the following screen is displayed.

The options are:


Updating the Levey-Jennings Chart with New Data

The Levey-Jennings chart can be easily updated with new data after it has been added to the spreadsheet. Please see Updating Control Charts with New Data to see how the software finds the new data and updates the chart.

Changing the Options for the Levey-Jennings Chart

You can change the current options for an existing Levey-Jennings chart (e.g., adding a Box-Cox transformation) by selecting “Options” on the Updating/Options panel on the SPC for Excel Ribbon.

The list of available charts in the workbook will be displayed. Select the chart you want to change options for. The input screen for that chart will be shown and changes can be made. See Changing Chart Options for more information.

In addition, once a control chart is made, there are numerous actions you can take on the chart including splitting control limits, removing points from the calculations, adding comments, selecting the range on which to base control limits, etc. Please see Control Chart Actions for details.

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