Graph tip - Creating a quality-control Levy-Jenning's graph with Prism.

This example explains how to create a Levy-Jennings QC graph with control lines, or grid lines, to mark the high and low control limits. This example also expains how to offset both X and Y axes, and in detail how to Hook Prism analysis constants to make custom grid lines.

How to do it:

Enter the data either onto an XY or Grouped table. Choose to enter single Y values (no subcolumns).

Double-click on either axis to open the Format Axes dialog. In the Frame and origin tab, choose to offset both the X and Y axes.

Click Analyze and choose Column statistics. This is in the list of Column analyses, but is ok to use for XY and Grouped data too. The default choices on the Column Statistics dialog will be fine.

Now, double click on the Y axis to open the Format Axis dialog. At the bottom of the dialog, click one of the buttons to bring up the Additional Ticks dialog. In Mac (shown here), the button is a gear. With Windows, the button is "...". 

Click the Fishhook icon to hook an analysis constant to define the coordinate of the custom grid line.

Choose the mean, and click OK.

Choose a grid line, with no tick. Choose its thickness, style and color.

When you click OK, Prism will take you back to the Format Axes dialog. Go to the next entry for Additional ticks and click Details.

In the Additional Ticks and Grid Details dialog, click the Fishhook, icon again. This time pick one of the QC control lines (mean plus or minus 1, 2 or 3 SD)s.

Choose a grid line, with no tick. Choose its thickness, style and color.

Repeat for all the control lines you want to draw.

Go back to the details dialog and you can choose to shade between the lines as you like.

Important note: Since the grid lines are hooked to the Column Statistics analysis, they will move if you add new data, edit data, or replace data with a new set of values.

Download this file if you would like to see how this graph was made.