I-MR-R/S (Between/Within) Chart

Test for Special Causes Results - I Chart

The Individuals (I) chart assesses whether the process location is in control. Each test for special causes detects points beyond the control limits and specific patterns in the data plotted on the I chart.

· When a subgroup fails a test, Minitab reports it in the Session window and marks it on the I chart. A failed subgroup indicates that there is a non-random pattern in the data that may be the result of special-cause variation. These subgroups should be investigated.

· When no points are displayed under the test results, no subgroups failed the tests for special causes.

Example Output

Test Results for MR Chart of Subgroup Means

TEST 1. One point more than 3.00 standard deviations from center line.

Test Failed at points: 14

Test Results for R Chart

TEST 1. One point more than 3.00 standard deviations from center line.

Test Failed at points: 8

Interpretation

For the injection molding data, no subgroups failed the tests for special causes on the I chart; therefore there is no evidence for lack of control in process location.