Control Chart

 

Menu location: Graphics_Control.

 

This plots the values of a process indicator over time (or some other sequence variable), and shows the variation within specified bands.

 

The bands show on a control plots are often called control limits and warning limits, denoting the type of action to be taken if values lie beyond them. A common application is the monitoring of laboratory processes, in which the warning limits are usually taken as two standard deviations (SD) either side of the mean and the control limits are three standard deviations either side of the mean (Mortimer, 1994, 1999).

 

StatsDirect offers the following options for control plot bands:

1. Optional display of mean (black), 1 SD (green), 2SD (black) and 3 SD (red) - [Default is all].
   
2. Mean and SD calculated from all process data - [Default].
   
3. Mean and SD calculated from the first k observations in the process data - [You specify k, for example basing the control standard on the first six months of operation when strict validation was performed].
   
4. Mean and SD specified - [Marked as 'external' on plot].
   
5. Control (red) and warning (black) limits specified - [Marked as 'external' on plot].

 

If your time/sequence data are dates then the x axis will be drawn as date labels vertically at the relevant data positions, using the short date format that is set in your Windows installation.