The Process Screening Report | JMP 13.2

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Predictive and Specialized Modeling • Process Screening • The Process Screening Report

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The Process Screening Report

The Process Screening report opens with a Summary table that contains results about process stability. It also contains capability results if you have provided specification limits. The processes and groups are initially sorted in decreasing order by Stability Ratio.

Tip: To sort the report by a column, click on the column name. A caret appears to the right of the column name. The direction of the caret indicates whether the sorting is descending or ascending. To change the order of the sorting, click on the column name again.

The control chart calculations in the Summary table include Nelson tests and a Range Limit Exceeded test. These tests assume the following about the control chart limits:

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The center line for the XBar or X control charts is given by the mean of all measurements or by the median of the observations if you use the Medians instead of Means option.

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Control limits are placed at three sigma units from the center line.

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Sigma is estimated using the conventions that correspond to the control chart type that you specified or, if you use Medians instead of Means, as described in Use Medians instead of Means.

Tip: The eight Nelson tests in the Process Screening platform follow the test settings in the Control Chart Builder platform preferences. You can customize the tests at File > Preferences > Platforms > Control Chart Builder.

The Summary table can contain the following information:

The columns that you entered as Process. There is a row for each distinct combination of Process and Grouping columns. This column is suppressed if there is only one process column.

Grouping Columns

There is a report column for each column in the data table that you entered as Grouping. The levels of the Grouping columns are listed so that there is a unique row in the report table for each distinct combination of Process name and Grouping columns values.

Contains the following columns:

Stability Ratio

A measure of stability of the process. The stability ratio is defined as follows:

(Overall Sigma/Within Sigma)2

A stable process has stability ratio near one. Higher values indicate less stability.

An estimate of the standard deviation based on within subgroup variation. The estimate is based on the control chart type that you specified, and is a short-term measure of variation. See Statistical Details for the Process Capability Platform in the Quality and Process Methods book for statistical details. If you select Medians instead of Means, Within Sigma is computed as described in Use Medians instead of Means.

The usual estimate of standard deviation based on all observations.

Contains the following columns:

(Appears only if you select Use Medians instead of Means in the launch window or if you import a Center value using a limits table.) The value listed under Centerline is used in control chart calculations as the center line.

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If you select Use Medians instead of Means in the launch window, the overall median of the observations is displayed.

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If you import a Center value from a limits table, that value is displayed.

The average of all observations.

The number of observations.

The number of subgroups.

Control Chart Alarms

Contains information on the subgroups that result in alarms for a variety of tests, including each of the 8 Western Electric rules. In the descriptions below, for an Indiv and MR chart, the single measurement is considered a subgroup of size 1. The standard deviation estimate is the Within Sigma value. By default, only the Alarm Rate, Test 1, and Latest Alarm columns are shown in the Summary table.

The number of subgroups that resulted in alarms for any of the tests selected under the Choose Test option (Any Alarm) divided by the number of subgroups (Subgroups).

(Appears only when more than one Test column is shown.) The number of subgroups that trigger alarms for any of the tests selected under the Choose Test option. These are the eight Nelson tests and the test for Range Limit Exceeded.

Tip: The eight Nelson tests in the Process Screening platform follow the test settings in the Control Chart Builder platform preferences. You can customize the tests at File > Preferences > Platforms > Control Chart Builder.

One point is more than three standard deviations from the center line. The subgroup associated with that point triggers the alarm.

Nine or more consecutive points are on the same side of the center line. The subgroup associated with the ninth point triggers the alarm.

Six or more consecutive points are continually increasing or decreasing. The subgroup associated with the sixth point triggers the alarm.

Fourteen consecutive points alternate in direction: increasing and then decreasing or decreasing and then increasing. The subgroup associated with the fourteenth point triggers the alarm.

Two out of three consecutive points on the same side of the center line are more than two standard deviations from the center line. The subgroup associated with the second point that exceeds two standard deviations triggers the alarm.

Four out of five consecutive points on the same side of the center line are more than one standard deviation from the center line. The subgroup associated with the fourth point that exceeds one standard deviation triggers the alarm.

Fifteen consecutive points, on either side of the center line, are all within one standard deviation of the center line. The subgroup associated with the fifteenth point triggers the alarm.

Eight consecutive points, on either side of the center line, all fall beyond one standard deviation of the center line. The subgroup associated with the eighth point triggers the alarm.

Range Limit Exceeded

The number of subgroups that exceed the upper control limit on the R, S, or MR chart calculation.

The position of the subgroup, counting from the last subgroup, that signaled the most recent alarm for any of the Nelson or Range Limit Exceeded tests.

(Appears only when there are Spec Limits specified for some processes.) Contains the following options:

Out of Spec Count

The number of observations that fall outside the specification limits.

Out of Spec Rate

The proportion of observations that fall outside the specification limits.

Latest Out of Spec

The number of observations, counting from the last observation, to the most recent observation that falls outside the specification limits.

Capability index based on Within Sigma and assuming a normal distribution. See Statistical Details for the Process Capability Platform in the Quality and Process Methods book for statistical details.

Capability index based on Overall Sigma and assuming a normal distribution. See Statistical Details for the Process Capability Platform in the Quality and Process Methods book for statistical details.

Shift Magnitudes and Positions

(Shown only if you have selected a Shift Detection option from the Process Screening red triangle menu.) Shift detection is performed to identify shifts that exceed one within-sigma unit. The algorithm uses outlier-correction and an exponentially-weighted moving average (EWMA) smoothing approach for the individual observations.

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Outliers are removed so that single outliers do not indicate shifts. The value specified as Outlier Threshold (five by default) on the launch window controls the sensitivity of outlier removal. If the number of within-sigma units from an observation to both of its neighboring observations exceeds the specified Outlier Threshold, that observation is replaced with a value that is one within-sigma unit away from its closest neighboring observation.

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An exponentially-weighted moving average (EWMA) fit is constructed for the subgroup means in forward time order and another EWMA fit is constructed for the subgroup means in reverse time order. The EWMA fits have lambda equal to 0.3.

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The largest positive and negative differences between successive EWMA values that exceed one within-sigma unit are identified.

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The absolute values of these differences, divided by the within estimate of sigma, are the values reported as Largest Upshift and Largest Downshift.

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The locations of the first subgroups involved in these largest shifts define the Upshift Position and Downshift Position.

Largest Upshift

The magnitude of the largest upward shift that exceeds one within-sigma unit, reported in within-sigma units.

Upshift Position or Upshift <Time Variable>

The position of the subgroup having the largest Upshift. If you specify a Time variable, the column in the Summary table is named Upshift <Time Variable> and the position of the shift is given in terms of the Time variable.

Largest Downshift

The magnitude of the largest downward shift that exceeds one within-sigma unit, reported in within-sigma units.

Downshift Position or Downshift <Time Variable>

The position of the subgroup having the largest Downshift. If you specify a Time variable, the column in the Summary table is named Downshift <Time Variable> and the position of the shift is given in terms of the Time variable.

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Help created on 9/19/2017