Overview of the Capability Platform
The Capability platform provides the tools needed to measure the compliance of a process to given specifications. By default, JMP shows a goal plot and capability box plot for each variable in the analysis. You can add normalized box plots, summary tables, capability indices, and an individual report for each variable in the analysis. Specification limits should be entered or available for each variable in the data table.
The individual detail reports include indices that help demonstrate a system’s ability to meet a set of requirements. Capability indices help change the focus from just meeting qualifications to continuous improvement of a process.
Capability analysis methods usually require that the data being studied is statistically stable, with no variation present. If a system is stable, capability analysis demonstrates the ability of the system in the past, and can also predict the system’s future performance.
The Capability platform has been replaced by the Process Capability platform. See “Process Capability” for more information about the new platform. The Capability platform has been removed from the Analyze > Quality and Process menu, and it is available only via scripting.
Note: The Process Capability platform expands significantly on the Capability analyses that are available through Analyze > Distribution and through Analyze > Quality and Process > Control Chart. By default, the Process Capability platform uses the appropriate AIAG notation for capability indices. It denotes an index constructed from an overall variation estimate using Ppk labeling. The previous Capability platform reported only overall variation with Cpk or Ppk labeling based on a platform preference. In the new platform, Cpk corresponds to within variation and Ppk corresponds to overall variation.
Launch the Capability Platform
Launch the Capability platform by submitting the following JSL:
Capability();
Figure 11.2 The Capability Launch Window for Semiconductor Capability.jmp
The Capability launch window contains the following options:
Y, Columns
Assigns the variables that you want to analyze.
Weight
Assigns a variable to give the observations different weights.
Freq
Assigns a frequency variable to this role. This is useful if you have summarized data.
By
Produces a separate report for each level of the By variable. If more than one By variable is assigned, a separate report is produced for each possible combination of the levels of the By variables.
Ignore columns with no spec limits
Prevents the Spec Limits window from appearing when the data table does not include spec limits for a selected variable.
After clicking OK, the Spec Limits window appears if you have not specified limits for the selected variables and Ignore columns with no spec limits is not selected. Otherwise, the report window appears.
Entering Specification Limits
The lower specification limit (LSL), upper specification limit (USL), and target define the lower bound, upper bound, and target value for a quality process.
There are several ways to enter spec limits:
• Enter limits in the Spec Limits window after selecting columns in the launch window. See “Spec Limits Window”.
• Import limits from a JMP data table (known as a Limits Table). See “Limits Data Table”.
• Enter limits as Spec Limits column properties in the data table. See “Spec Limits Column Property”.
Only one spec limit is required for a selected column. If only the upper spec limit (USL) is specified, the box plot is colored blue. If only the lower spec limit (LSL) is specified, the box plot is colored red.
Spec Limits Window
After you click OK on the launch window, the Spec Limits window appears if the data table does not contain limits for the selected columns and you did not select Ignore columns with no spec limits on the launch window. Figure 11.3 shows the Spec Limits window for the Cities.jmp sample data table after selecting OZONE, CO, SO2, and NO in the launch window. Enter the known spec limits and click Next to view the reports.
Figure 11.3 Spec Limits Window for Cities.jmp
Limits Data Table
You can also retrieve a limits data table with the Import Spec Limits option from the Spec Limits red triangle menu. Select Import Spec Limits and then select the appropriate data table that contains the specification limits for the analysis. After selecting the appropriate limits table, the values populate the window. Click Next to continue to the reports window.
All limits data tables must have a column for each of the variables whose values are the known standard parameters or limits. A limits data table can be in two different formats: wide or tall. Either you have a column for each response with the limits key or you have one column for each response and the limits key words are the columns. Either of these formats can be read using the Import Spec Limits command. Figure 11.4 shows an example of both types of limits data tables.
Figure 11.4 Wide (Top) and Tall (Bottom) Spec Limit Tables
• A wide table contains one column for each column analyzed in the Capability platform, with three rows plus a _LimitsKey column. In the _LimitsKey column, the three rows need to contain the identifiers _LSL, _USL, and _Target.
• A tall table contains one row for each column analyzed in the Capability platform, with four columns. The first column holds the column names. The other three columns need to be named, _LSL, _USL, and _Target.
The easiest way to create a limits data table is to save results computed by the Capability platform. The Save Spec Limits command in the Capability red triangle menu automatically saves limits from the sample values. After entering or loading the specification limits, you can save the limits in the following ways:
• Save the limits to the data table by selecting Save Spec Limits as Column Properties.
• Save the limits to a new wide data table, with a column for each analyzed column, by selecting Save Spec Limits in New Table.
• Save limits to a new tall data table, with a row for each analyzed column, by selecting Save Spec Limits in New Table - Tall. Consider this option for tables that have hundreds of variables.
For more information, see “Capability Platform Options”.
Spec Limits Column Property
When you perform a capability analysis, you do not have to re-specify the limits each time. Use the Column Properties > Spec Limits property in a data table to save specification limits as a column property. Saving these limits in a column also facilitates consistency from use to use. For example, you might run an analysis that uses these limits. When you come back later and change the data, you can run a new analysis on the new data using the same limits. Figure 11.5 displays the Spec Limits section of the Column Properties window for OZONE in the sample data table Cities.jmp.
Enter a lower and upper specification limit and a target value for a numeric column. Ideally, the process variation is between the LSL and USL.
The Show as graph reference lines option draws specification limits as reference lines on a graph. For more information about column properties, refer to the Column Info Window chapter in the Using JMP book.
Figure 11.5 Spec Limits Section of the Column Properties Window
The Capability Report
By default, the Capability report contains two main sections:
Using the Capability red triangle menu, you can add normalized box plots, capability indices, and a summary table, as well as display a capability report for each individual variable in the analysis. These options are described in “Capability Platform Options”.
You can change the report default preference at File > Preferences > Platforms > Capability.
Figure 11.6 Default Results for Semiconductor Capability.jmp
Goal Plot
The Goal Plot shows, for each variable, the spec-normalized mean shift on the x-axis, and the spec-normalized standard deviation on the y-axis. It is useful for getting a quick, summary view of how the variables are conforming to specification limits. Hold your cursor over each point to view the variable name. The Goal Plot red triangle menu has the following commands:
Shade CPK Levels
Shows or hides the CPK level shading.
Goal Plot Labels
Shows or hides the labels on the points.
Defect Rate Contour
Shows or hides a contour representing a specified defect rate.
Figure 11.7 shows the Goal Plot for the entire data set for the Semiconductor Capability.jmp sample data table after selecting Shade CPK Levels from the Goal Plot red triangle menu.
Figure 11.7 Goal Plot
For each column with LSL, Target, and USL, these quantities are defined as follows:
Mean Shift Normalized to Spec = (Mean(Col[i]) - Target) / (USL[i] - LSL[i])
Standard Deviation Normalized to Spec = Standard Deviation(Col[i])/ (USL[i] - LSL[i])
By default, the CPK slider and number edit box is set to CPK = 1. This approximates a non-conformance rate of 0.0027, if the distribution is centered. The red goal line represents the CPK shown in the edit box. To change the CPK value, move the slider or enter a number in the edit box. Points on the plot represent columns, not rows.
The shaded areas are described as follows, with C representing the value shown in the CPK edit box:
• Points in the red area have CPK < C.
• Points in the yellow area have C < CPK < 2C.
• Points in the green area have 2C < CPK.
JMP has a preference for plotting PPK instead of CPK. When this is on, the slider is labeled with PPK. You can change the preference at File > Preferences > Platforms > Capability.
Capability Box Plots
The Capability Box Plots show a box plot for each variable selected in the analysis. The values for each column are centered by their target value and scaled by the difference between the specification limits. For each column Yj:
with Tj being the targetFigure 11.8 Capability Box Plot
Figure 11.8 shows the Capability Box Plot for the Semiconductor Capability.jmp sample data table. The left and right dotted green lines, drawn at ±0.5, represent the standardized LSLj and USLj respectively. This plot is useful for comparing variables with respect to their specification limits. For example, the majority of points for IVP1 are above its USL, while the majority of its points for IVP2 are less than its target. PNP2 looks to be on target with all data points in the spec limits.
Missing Spec Limits
When a spec limit is missing for a column, the box plot is colored. If only the upper spec limit (USL) is specified, the box plot is colored blue. If only the lower spec limit (LSL) is specified, the box plot is colored red. See Figure 11.9. A note at the bottom of the plot describes the calculations used for the plot.
Figure 11.9 Missing Spec Limits
Capability Platform Options
The following options are accessed by clicking the Capability red triangle menu in the report window:
Goal Plot
Shows a goal plot for the data. The Goal Plot shows the spec-normalized mean shift on the x-axis, and the spec-normalized standard deviation on the y-axis for each variable. See “Goal Plot” for more information.
Normalized Box Plots
Shows a normalized box plot for the data. Each column is standardized by subtracting off the mean and dividing by the standard deviation, and quantiles are formed for each standardized column. The box plots are formed for each column from these standardized quantiles. See “Normalized Box Plots” for more information.
Capability Box Plots
Shows a capability box plot for each variable in the analysis. The values for each column are centered by their target value and scaled by the difference between the specification limits. See “Capability Box Plots” for more information.
Make Summary Table
Makes a summary table for the data that includes the variable’s name, its spec-normalized mean shift, and its spec-normalized standard deviation. See “Make Summary Table” for more information.
Capability Indices Report
Shows a capability indices report for the data showing each variable’s LSL, Target, USL, Mean, Standard Deviation, Cp, CPK, and PPM. See “Capability Indices Report” for more information.
Individual Detail Reports
Shows individual detail reports for each variable in the analysis. See “Individual Detail Reports” for more information.
Order By
Enables you to reorder box plots, capability indices reports, and individual details reports. You can reorder by Initial Order, Reverse Initial Order, CPK Ascending, or CPK Descending.
Save Spec Limits
Enables you to save specification limits for the data. See “Limits Data Table”.
See the JMP Reports chapter in the Using JMP book for more information about the following options:
Local Data Filter
Shows or hides the local data filter that enables you to filter the data used in a specific report.
Redo
Contains options that enable you to repeat or relaunch the analysis. In platforms that support the feature, the Automatic Recalc option immediately reflects the changes that you make to the data table in the corresponding report window.
Save Script
Contains options that enable you to save a script that reproduces the report to several destinations.
Save By-Group Script
Contains options that enable you to save a script that reproduces the platform report for all levels of a By variable to several destinations. Available only when a By variable is specified in the launch window.
Normalized Box Plots
When drawing Normalized Box Plots, JMP first standardizes each column by subtracting off the mean and dividing by the standard deviation. Next, quantiles are formed for each standardized column. The box plots are formed for each column from these standardized quantiles.
Figure 11.10 Normalized Box Plot
Figure 11.10 shows the Normalized Box Plot for the Semiconductor Capability.jmp sample data table.
The green vertical lines represent the spec limits normalized by the mean and standard deviation. The gray dotted vertical lines are drawn at ±0.5, since the data is standardized to a standard deviation of 1.
Make Summary Table
The Make Summary Table option produces a summary table that includes the variable’s name, its spec-normalized mean shift, and its spec-normalized standard deviation for further evaluation.
Figure 11.11 shows the Summary Table for the Semiconductor Capability.jmp sample data table.
Figure 11.11 Summary Table
Capability Indices Report
The Capability Indices Report option shows or hides a table showing each variable’s LSL, Target, USL, Mean, Standard Deviation, Cp, CPK, and PPM. Figure 11.12 shows the Capability Indices for the Semiconductor Capability.jmp sample data table. Optional columns for this report include Lower CI, Upper CI, CPM, CPL, CPU, PPM Below LSL, and PPM Above USL, among others. To reveal these optional columns, right-click on the report and select the column names from the Columns submenu.
Figure 11.12 Capability Indices
Individual Detail Reports
The Individual Detail Reports option displays a capability report for each variable in the analysis. This report is identical to the Capability Analysis Report from the Distribution platform, detailed in the Distributions chapter in the Basic Analysis book. Figure 11.13 shows the Individual Detail Report for PNP1 from the Semiconductor Capability.jmp sample data table.
Figure 11.13 Individual Detail Report
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