Go to Graph à Control Chart à XBar, and put “turnaround time” in “Process”, “day” in “Sample Label”, and add “Phase” in the “Phase” box, as follows: You can also use a Phase variable in the control chart. The data table we are using in this example also contained a “Phase” variable that indicated pre-intervention versus post-intervention days. Using a Phase Variable in a Control Chart The XBar chart will now contain all the data points, and special cause tests that are met will be highlighted and labeled as follows: If any of the special cause tests are met, the point will be highlighted in the control chart and the test number will appear next to it.įor example, you can go back to the data table and unexclude and unhide the days of the intervention (rows 19 till 69), by clicking on Rows à Clear Row States. If you place your mouse on one of the tests, for example Test 1, the definition of that test will appear, such as “One point beyond Zone A”. This will turn on all special cause tests. Turning on the Special Cause TestsĬlick on the little red triangle next to “Xbar of turnaround time” and select Tests à All Tests. Typically, if you are collecting data in real time, after freezing the control limits, you would turn on all special cause tests to be able to detect changes instantaneously. To unfreeze the control limits, you need to delete the “Sigma” and “Limits” properties from the column, by right-clicking on the variable name and choosing “Column Info”, and under “Properties”, removing these 2 properties. This will save the control limits as properties in the “turnaround time” process variable, as indicated by the asterisk symbol now appearing next to the variable in the data table. To freeze the control limits to their values based on these 6 days, click on the little red triangle next to “Variables Control Chart” and click “Save Limits” à “In Column”. Notice the note on the bottom: “17 samples were excluded”. The XBar chart now only contains data up to Day 6. Redo the XBar Control Chart following the instructions in part 1 ( Graph à Control Chart à XBar put “Day” in “Sample Label” and “turnaround time” in “Process” click OK). This will exclude and hide rows 19 through 69, as shown in the following picture. On the top menu, click on ROWS à Exclude/Unexclude then ROWS à Hide/Unhide. To do that, select all the post-intervention rows, starting at Day 7 (row 19) till the end of the table. You know that you will implement an intervention on Day 7, and you want to be able to freeze the control limits to what they are in baseline, so that you can visualize whether or not any change is taking place after you intervene, compared to baseline. You want to plot the data that you have collected so far on the first 6 days, to look at your process at baseline and judge whether it is in control. Suppose you were collecting your data in real time, and you are at Day 6. Click “Add” then “Ok”.Ī blue reference line will now be added on the X axis, labeled as “Intervention”, as follows:įreezing Control Limits in a Control Chart
Click on the black square next to Color and pick a different color, such as blue. Under “Reference Lines”, type “8” in “Value” and type “Intervention” in “Label”. Double-click on the X axis to open the “X Axis Specification” menu. Suppose you want to add a reference line on the X-axis that indicates the start of the intervention, on Day 7. To color the zones, click on the same red triangle as before and choose “Shade Zones”: If you want to add the control zones, click on the little red triangle next to “XBar of turnaround time”Ĭlick on “Show Zones” to show zones A, B, and C around the centerline, as follows: The X axis represents day the Y axis represents the AVERAGE turnaround time for each day. The average, upper, and lower control limits are shown on the XBar chart. You will get an XBar Control Chart and a Range Chart, as follows: Put “Day” in the “Sample Label” and “Turnaround Time” in the “Process”, as shown in the following picture. To make an XBar Control Chart using all the data available in JMP, go to Analyze>Quality and Process>Control chart>XBAR. On Day 7 (observation number 19), an intervention takes place to reduce turnaround time. There are several measurements of turnaround time within a single day therefore, you can make an XBar Control Chart. Example: You have a dataset with the variables Day, Turnaround Time, and Phase.
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