Levey Jennings Plots
Contents
A Levey Jennings Plot allows you to visualize quality control data to ensure test metrics are stable over time and fall within a predetermined range. The range, more commonly referred to as the control limits, allows the test metric to be assessed based on whether the values fall within the range or outside of the range. Values falling outside of the control limits are considered "out of control" and when occurring on consecutive measurements can indicate the accuracy of the test metric has shifted. Special rules, called the "Westgard Rules", are often applied to interpret the Levey Jennings Plot.
Levey Jennings Plots are built from an existing Spreadsheet in your layout. The Spreadsheet must contain two parameters, typically represented as the time (X parameter) and test metric (Y parameter).
The spreadsheet can be populated by
•Manual insertion
•Inserting Tokens by Dragging and Dropping Files from the Data List
•Batch Processing to Spreadsheet
An example of data set suitably arranged within a Spreadsheet and the resulting Levey Jennings Plots is shown below (Figure 5.262). Please note that when dates have to be plotted on the X axis, said dates has to be manually entered into the spreadsheet and the cells containing said dates, have to be properly formatted with the Date format.
Figure 5.260 A Spreadsheet with data for a Levey Jennings Plot
To insert a Levey Jennings Plot from an existing Spreadsheet:
1. Select a Spreadsheet in the Layout.
2. Click the Insert tab→2D Plots→Other→Levey Jennings command.
3. Click on a blank space of the layout to insert the Levey Jennings Plot.
By default, the Levey Jennings Plot will plot the first two columns of the Spreadsheet for the X Parameter and Y Parameter, respectively. To populate the Levey Jennings Plot with parameters other than the first two columns of the Spreadsheet, either:
•Click on the axis parameter name within the plot and select the intended parameter from the list of available parameters or,
•Change the X and/or the Y Parameters from the Overlay Formatting dialog (See instructions below)
To change the X and/or the Y parameters on the scatter plot via the Overlay Formatting dialog, use the appropriately named X (or Y) Parameter dropdown menus shown below (Figure 5.263, 
) and further described in the accompanying table.
Figure 5.261 Levey Jennings Plot Overlays
Additional formatting options for depicting data points, Westgard rules, In and Out of Control Points, mean line, and control limits are described in the table below.
Option |
Explanation |
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The parameter (i.e., Spreadsheet column) intended for the X & Y parameters is set using the appropriately named ... Parameter dropdown menus. For Levey Jennings Plots, the Y parameter is treated as the test metric. |
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The points for the test metric on Levey Jennings plots have the following options: ▪Connect the points - Draws a connecting line between each point. ▪Visible - Show or Hide the Levey Jennings Plot. ▪Show marks - Displays the test metric value above each point. |
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Select which parameter(s) to draw the control lines. Control lines can be drawn for the X parameter, Y parameter, or both X & Y parameters simultaneously ( |
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Select the Westgard rules to determine out of control events. More than one option may be selected. Any value(s) meeting the selected criteria for out of control events will be highlighted. Note that the mean of the test metric (Y parameter) will be used as the control value when applying the Westgard rules.
The following options are available: ▪1:2s - One value beyond +/- 2 standard deviations from the mean. ▪1:3s - One value beyond +/- 3 standard deviations from the mean. ▪2:2s - Two consecutive values either greater than, or less than, 2 standard deviations from the mean. ▪r:4s - One value beyond +2 standard deviations from mean and the following value beyond -2 standard deviations or vice-versa. ▪4:1s - Four consecutive values greater than, or less than, one standard deviations from mean. ▪10:x - Ten consecutive values all greater than, or less than, the mean. |
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The Shapes for the following plot elements may be defined: ▪In-Control Point: data points which are within the control limits according to the selected Westgard Rules. ▪Out of Control Point: data points which are out of control limits according to the selected Westgard Rules.
The available shapes include "Rectangle", "Triangle", "Circle", etc., and are shown in the Shape ( |
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The Lines for the following plot elements may be defined:
▪Point Border: the border line for In Control points. ▪Connecting Lines: the line connecting all points on the plot. The color selected for In-Control Points can be applied using the checkbox. ▪Out of Control Point Border: the border line for Out of Control points. ▪Mean Line: the line corresponding to the Y parameter (test metric) mean value. See green solid line above. ▪1*SD from Mean: the line corresponding to 1 standard deviations from the Y parameter (test metric) mean. See blue dashed line above. ▪2*SD from Mean: the line corresponding to 2 standard deviations from the Y parameter (test metric) mean. See orange dashed line above. ▪3*SD from Mean: the line corresponding to 3 standard deviation from the Y parameter (test metric) mean. See red solid line above.
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