Quality Control Charts (Counts and Proportions)

The Quality Control Charts (Counts and Proportions) dialog creates quality control charts for counts (number of defective samples) and proportions (proportion of defective samples).

Choose Statistics __image\arrow5.gif Quality Control Charts __image\arrow5.gif Counts and Proportions. The dialog shown below appears.

Model page

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In the Quality Control Charts (Counts and Proportions) 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.

Batch Size Type

For these charts every row of data represents a group. If the batch size is the same for all groups, it can be specified by setting Batch Size Type to Equal and entering it in the Batch Size field. Otherwise, a column of batch sizes will be used.

Size Column

Specify the column giving the batch size for each observation.

Batch Size

Specify the batch size used for the observations.

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

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.

Groups (This is available for QCC Continuous Grouped and Counts and Proportions only.) Used when Groups is selected as the Calibration Type. To specify the groups used for calibration, you can specify an index vector of groups (such as 1:10 for the first 10 days in the above example), or use the drop-down list to select specified groups.

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

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In the Quality Control Charts (Counts and Proportions) 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

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In the Quality Control Charts (Counts and Proportions) dialog, the Results page has the following options:

Plots

Shewhart Select to plot a Shewhart chart.

Cusum Select to plot a Cusum 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.

Cusum Options

Decision Interval A numeric value in number of standard errors of the summary statistics at which the cumulative sum signals out of control.

SE Shift The amount of shift to detect in the process measured in standard errors of the summary statistics. Twice what is referred to as the reference value which is the amount a summary statistic must exceed the target value in absolute value before it is added to the cumulative sum.

Reset when out of control Check this box to reset the cumulative sum after an out-of-control signal.

Headstart Value If the Reset when out of control box is selected, you may optionally specify a numeric value in standard errors of the group summary statistics at which to start the cumulative sums. The default is to use half the decision interval.

 

S-Plus language functions related to Quality Control Charts

qcc, shewhart, cusum