As a manufacturing engineer I was introduced to the wonderful world of control charts so I have constructed these to see if our current winter UK rainfall was exceptional.
The ASQ (American Society for Quality) suggests these criteria for an out of control process:
- A single point outside the control limits.
- Two out of three successive points are on the same side of the centreline and farther than 2s
- Four out of five successive points are on the same side of the centreline and farther than 1s
- A run of eight in a row are on the same side of the centreline.
- Obvious consistent or persistent patterns that suggest something unusual about your data and your process.