Creates a quality control chart.
In this chart the data are plotted consecutively, together with a line at the mean, and at -2s, +2s, -3s and +3s (s = standard deviation), i.e. at 95% and 99.7% confidence limits.
In the Control chart dialog box you define the data to be represented in the quality control chart. First, enter the variable's name in the variable input field. Optionally, you may also enter a selection criterion in order to include only selected data in the graph, e.g. measurements by a particular technician. Also you can enter a variable containing labels for the X-axis (e.g. dates).
Next select the type of control limits:
When you have completed the dialog box, click the OK button to proceed.
In the following example, a control chart is created for the technician with code 2.
The result is displayed in the following figure:
Custom control chart
When there are no data available for the variable, the program will ask whether you want to create a custom control chart, i.e. a blank control chart that you can print and on which the lab technician can mark the control measurements manually.
When you click the SELECT RULES button, the following dialog box is displayed, in which you can select a combination of rules to be applied in the control chart:
If you select the 1:2S rule then the software will check all following rules only if the measurement exceeds the mean ± 2SD (or the warning limits).
If the measurement exceeds the mean + 3SD or mean - 3SD, then the run is considered out of control.
The run is considered out of control when 2 consecutive measurements exceed the same mean + 2S or the same mean - 2S limit.
The run is considered out of control when 4 or more consecutive measurements exceed the same (mean + 1S) or (mean - 1S) limit.
The run is considered out of control when 10 or more consecutive measurements are on the same side of the mean. The software allows you to select a different value less than 10 for a higher sensitivity or more than 10 for a lower sensitivity of this rule.
When the option Apply rules is selected in the Control chart dialog box, and the 1:3S rule is selected in the Multirules dialog box, then when a measurement exceeds the mean + 3SD or mean - 3SD, this value will be clearly indicated in the graph (using a red marker). Click the value to display information on this measurement: