Two other tools, the run chart and the histogram, are also used to monitor the process. These tools are easy to set up and maintain and don’t require the statistical calculations found in a control chart.
The run chart plots an individual metric over time and makes it easy to spot trends and patterns over time.
Here are some things to look for in a run chart that may indicate an unstable or problem process:
- Cluster: Several observations surrounding a certain value
- Mean shift: Several observations above or below the process average
- Oscillations: Observations that go up and down with recognizable frequency
- Trends: Several observations in a row that all go up or down