Quality Control Charts (Continuous Ungrouped)
The Quality Control Charts (Continuous Ungrouped) dialog creates quality control charts of exponentially weighted moving averages (ewma), moving averages (ma), moving standard deviations (ms), and moving ranges (mr). These charts are appropriate when variation is determined using sequential variation rather than group variation.
Choose Statistics Quality Control Charts
Continuous Ungrouped from the main menu. The dialog shown below appears.
Model page
In the Quality Control Charts (Continuous Ungrouped) dialog, the Model page has the following options:
Data
Data Set
Select a data set from the dropdown list or type the name of a data set. You can also type into the Data Set edit field any expression that evaluates to a data set.
Variable
Select the variable to chart.
Chart Type
Type
Select the type of chart to be created. You can choose from the following charts:
Type |
Common name |
Statistic |
xbar |
x-bar |
Mean within group |
s |
s Chart |
Standard deviation within group |
r |
R or Range Chart |
Range within group |
Averaging Options
Averaging Method Specify the averaging method to use. Either simple or exponential moving averages are available for xbar charts. Only simple moving averages are available for R and s charts.
Sigma Method Specify whether the standard deviation or range should be used for computing variation.
Span for Sigma Specify the span for the moving estimate of variance.
Span for Stat Specify the span for the moving estimate of the statistic of interest.
Exp Weight Specify a weight to use in the exponentially weighted moving average.
Calibration
Type By default, the control limits are calculated using all the data available. But when the process is going out of control, this may make the control limits too wide. To calibrate the control limits based on a subset of the data, or other data, use another calibration type.
Saved Object Used when Saved is selected as the Calibration Type. You can save the calibration results in a QCC object by entering an object name in the Save As field. This calibration may then be used for future charts by specifying Saved as the Calibration Type, and selecting the saved object in the Saved Object field.
Save Calibration Object
Save As Specify a name under which to save the calibration results. These results may then be used later by creating a chart using Type set to Saved.
Results page
In the Quality Control Charts (Continuous Ungrouped) dialog, the Results page has the following options:
Printed Results
Calibration Summary Select to print a summary of the calibration object.
Chart Summary Select to print a summary of the charted data.
Capability Select to print estimates of capability.
Capability Options
Allowable Range Specify the allowable range for which to calculate capability.
Lower Limit Specify the lower limit for which to calculate capability.
Upper Limit Specify the upper limit for which to calculate capability.
Plot page
In the Quality Control Charts (Continuous Ungrouped) dialog, the Results page has the following options:
Plots
Shewhart Select to plot a Shewhart chart.
General Options
Include Statistics By default, various statistics are printed at the bottom of both charts. Clear this option to prevent these statistics being included. This allows more room on the page for the actual chart.
Include Calibration Data If you did not use the Self option for calibration, by default the calibration data and the new data are plotted on the charts. To plot only the new data, clear this option.
Target Override By default, the target line is calculated using the calibration data. To override this and specify your own target value, enter it here.
Std Dev Override Similarly, by default the control limits and decision boundaries are calculated using the variation in the calibration groups. To specify a fixed standard deviation, enter it here.
Shewhart Options
Limits Type The confidence limits may be specified in terms of a confidence level, number of sigmas, or upper and lower limit values.
Confidence Level Specify the confidence level used to calculate the control limits.
Number of Sigmas Specify the width of the control limits as multiples of the standard deviation from the target value.
Lower Limit Specify the lower confidence limit value.
Upper Limit Specify the upper confidence limit value.
Max Run Length If there is a run of chart values consecutively above or below the target value they will be highlighted using a different color. This control specifies how many consecutive values to observe before highlighting values. By default, the fifth consecutively high or low value is highlighted.
S-Plus language functions related to Quality Control Charts
qcc, shewhart, cusum