Publication date: 04/12/2021

Control Chart Type

Select one of five control chart types: Indiv and MR (Individual Measurement and Moving Range); XBar and R; XBar and S; XBar, MR, and R; or XBar, MR, and S. The XBar, MR, and R control chart and the XBar, MR, and S control chart are also referred to as three way control charts. For more information about statistical details, see Statistical Details for Control Chart Builder in Quality and Process Methods.

Note: The three way control charts are available only when the subgroup sizes are bigger than 1. If a three way control chart is selected and the subgroup sizes are 1, an error message appears.

Note: If the subgroup size for a process is 1, the chart automatically switches to an Indiv and MR chart.

Subgroup Sample Size

Specifies a constant sample size for subgroups. The minimum subgroup size is 2. A subgroup size of 5 is the default. The Subgroup Sample Size specification is ignored for Indiv and MR charts or when a subgroup variable is specified.

KSigma

Specifies the sigma multiplier. KSigma is the value that is multiplied by sigma in the calculation of control limits. By default, KSigma is 3.

Use Limits Table

Enables you to import historical control limits and specification limits from a data table. When you select this option and click OK in the launch window, a Choose limits table window appears. Once you choose a limits tables and click OK, a Limits Specification window appears. Assign columns in your limits table to appropriate roles and click OK. See Limits Table.

Note: If you do not select this option, limits are obtained from the Control Limit and Specification Limit column properties for the Process Variables. If you do not select this option and the Process Variables do not have control limit column properties, the control limits are calculated from the data.

Use Medians instead of Means

Estimates the center line using the median of the observations. Sigma is estimated using scaling factors obtained using Monte Carlo simulation. The table of factors is given in Statistical Details for the Process Screening Platform. The calculation depends on the type of chart selected:

– For XBar and R chart or Indiv and MR chart calculations, sigma is estimated using the scaled median of the ranges.

– For XBar and S chart calculations, sigma is estimated using the scaled median of the standard deviations.

– For unequal subgroup sizes, the scaling factor corresponds to the average subgroup size rounded to the nearest integer.

When one or more outliers influence the location of the center line, many subgroups can appear out of control. Using the median alleviates this problem.

Note: When Use Medians instead of Means is selected, the results obtained from the Control Charts for Selected Items or the Process Capability for Selected Items red triangle menu options do not match the Process Screening results.

Advanced Options

Contains the following options:

Shift Threshold

Specify a value that controls the sensitivity of the Shift Graph. Shift Threshold is set to three by default. After outlier removal, the Shift Graph shows a plot of the time occurrence of all process shifts that exceed the number of within-sigma units specified by the Shift Threshold. See Shift Graph.

Outlier Threshold

Specify a value that controls the sensitivity of outlier removal for detection of large recent shifts and for the Shift Graph. Outlier Threshold is set to five by default. 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. See Shift Magnitudes and Positions.

Shift Lambda

Enables you to change the exponentially weighted moving average (EWMA) weight used in the Shift Graph. See Shift Magnitudes and Positions.

Drift Beta

The weight used in the exponentially weighted moving average (EWMA) for drift detection. Drift Beta is set to 0.05 by default.

Minimum Process Length

The minimum number of data values that a process must have in order to be included in the analysis. By default, this value is set to 3.

Want more information? Have questions? Get answers in the JMP User Community (community.jmp.com).