Definition of Voice of the Process (VOP):
Term used to describe what the process is telling you. What it is capable of achieving, whether it is under control and what significance to attach to individual measurements – are they part of natural variation or a signal that needs to be dealt with?
The best way to discover the VOP is to plot it on a control chart – time sequenced events across the bottom (x-axis) and the individual results up the side (y-Axis). Calculate the normal variation ranges and plot these as lines above and below the average the process is giving you.
Any points within the lines are part of the normal variation and any points above and below the lines have ‘special causes’ which are the only ones worthy of investigation and action. Minitab or WINCHART software does all this plotting for you.