Enables you to enter control limits for tests. After you click OK in the Set Control Limits window, the specified control limits are set uniformly across groups. Select this option again to remove the specified control limits.
Adds a dispersion chart to the chart area. Change the chart type with the Points options. A dispersion chart illustrates the variation in the data by plotting one of many forms of dispersion, including the range, standard deviation, or moving range. Available only for Variables chart types.
Note: For a description of the Rows, Graph, Customize, and Edit menus, see the Using JMP book.
The Warnings option in the right-click menu or on the left hand side of the window displays a submenu for Tests selection. You can select one or more tests for special causes (Western Electric rules) from the menu. Nelson (1984) developed the numbering notation used to identify special tests on control charts. The tests work with both equal and unequal sample sizes.
Table 2.8 lists and interprets the eight tests, and Figure 2.7 illustrates the tests. The following rules apply to each test:
 • The area between the upper and lower limits is divided into six zones, each with a width of one standard deviation.
 • The zones are labeled A, B, C, C, B, A with zones C nearest the center line.
 • A point lies in Zone B or beyond if it lies beyond the line separating zones C and B. That is, if it is more than one standard deviation from the center line.
 • Any point lying on a line separating two zones lines is considered belonging to the innermost zone. So, if a point lies on the line between Zone A and Zone B, the point is considered to be in Zone B.
Notes:
 • Tests 1 through 8 apply to all Shewhart chart types.
 • Tests 1, 2, 5, and 6 apply to the upper and lower halves of the chart separately.
 • Tests 3, 4, 7, and 8 apply to the whole chart.
 • Once a runs test (one that is based on consecutive observations) is triggered, the counts do not reset to 0 when moving to the next sample.
 • Because excluded observations change the sample, the excluded state of a row is not considered for runs tests (ones that are based on consecutive observations).
See Nelson (1984, 1985) for further recommendations on how to use these tests.
Figure 2.6 Zones for Western Electric Rules
 Test 1 One point beyond Zone A Detects a shift in the mean, an increase in the standard deviation, or a single aberration in the process. For interpreting Test 1, any dispersion chart (R-, S-, or MR-) can be used to rule out increases in variation. Test 2 Nine points in a row in a single (upper or lower) side of Zone C or beyond Detects a shift in the process mean. Test 3 Six points in a row steadily increasing or decreasing Detects a trend or drift in the process mean. Test 4 Fourteen points in a row alternating up and down Detects systematic effects such as two alternately used machines, vendors, or operators. Test 5 Two out of three points in a row in Zone A or beyond and the point itself is in Zone A or beyond. Detects a shift in the process average or increase in the standard deviation. Any two out of three points provide a positive test. Test 6 Four out of five points in a row in Zone B or beyond and the point itself is in Zone B or beyond. Detects a shift in the process mean. Any four out of five points provide a positive test. Test 7 Fifteen points in a row in Zone C, above and below the center line Detects stratification of subgroups when the observations in a single subgroup come from various sources with different means. Also detects a reduction in variation. Test 8 Eight points in a row on both sides of the center line with none in Zones C Detects stratification of subgroups when the observations in one subgroup come from a single source, but subgroups come from different sources with different means.

Nelson (1984, 1985)

Figure 2.7 Illustration of Special Causes Tests1
Westgard rules are implemented under the Westgard Rules submenu of the Warnings option when you right-click on a chart or on the left hand side of the window. The different tests are abbreviated with the decision rule for the particular test. For example, 1 2s refers to a test where one point is two standard deviations away from the mean.
Notes:
 • Once a runs test (one that is based on consecutive observations) is triggered, the counts do not reset to 0 when moving to the next sample.
 • Because excluded observations change the sample, the excluded state of a row is not considered for runs tests (ones that are based on consecutive observations).
Rule 1 2S is commonly used with Levey-Jennings charts, where control limits are set 2 standard deviations away from the mean. The rule is triggered when any one point goes beyond these limits.
Rule 1 3S refers to a rule common to Levey-Jennings charts where the control limits are set 3 standard deviations away from the mean. The rule is triggered when any one point goes beyond these limits.
Rule 2 2S is triggered when two consecutive control measurements are farther than two standard deviations from the mean.
Rule R 4S is triggered when one measurement is greater than two standard deviations from the mean and the previous measurement is greater than two standard deviations from the mean in the opposite direction such that the difference is greater than 4 standard deviations.
Rule 4 1S is triggered when four consecutive measurements are more than one standard deviation from the mean.
Rule 10 X is triggered when ten consecutive points are on one side of the mean.

Nelson 1984, 1985)

Help created on 7/12/2018