Example of I-MR chart main topic interpreting results session command see also
Example of I-MR chart As the distribution manager at a limestone quarry, you want to monitor the weight (in pounds) and variation in the 45 batches of limestone that are shipped weekly to an important client. Each batch should weigh approximately 930 pounds. You previously created a Moving Average chart. Now you want to examine the same data using an individuals and moving range chart.
1 Open the worksheet EXH_QC.MTW.
2 Choose Stat > Control Charts > Variables Charts for Individuals > I-MR.
3 In Variables, enter Weight.
4 Click I-MR Options, then click the Tests tab.
5 Choose Perform all tests for special causes, then click OK in each dialog box.
Session window output
I-MR Chart of Weight
Test Results for I Chart of Weight
TEST 1. One point more than 3.00 standard deviations from center line. Test Failed at points: 14, 23, 30, 31, 44, 45
TEST 2. 9 points in a row on same side of center line. Test Failed at points: 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 33, 34, 35, 36
TEST 5. 2 out of 3 points more than 2 standard deviations from center line (on one side of CL). Test Failed at points: 24, 30, 31, 45
TEST 6. 4 out of 5 points more than 1 standard deviation from center line (on one side of CL). Test Failed at points: 5, 6, 7, 29, 30, 31, 32, 45
Test Results for MR Chart of Weight
TEST 1. One point more than 3.00 standard deviations from center line. Test Failed at points: 25
* WARNING * If graph is updated with new data, the results above may no * longer be correct. |
Graph window output
The individuals chart shows 6 points outside the control limits and 22 points inside the control limits exhibiting a nonrandom pattern, suggesting the presence of special causes. The moving range chart shows one point above the control limit. You should closely examine the quarry's processes to improve control over the weight of limestone shipments.