Use I-MR Chart to monitor the mean and variation of your process when you have continuous data that are individual observations not in subgroups. Use this control chart to monitor process stability over time so that you can identify and correct instabilities in a process.
For example, a hospital administrator wants to determine whether the time to perform outpatient hernia surgery is stable and whether the variation in surgery times is stable. Because the data are not collected in subgroups, the administrator uses an I-MR chart to monitor the mean and variation of the surgery times. On both charts, the points vary randomly around the center line and are within the control limits. No trends or patterns are present. The amount of time to perform hernia surgery and the variation in times are stable.
Where to find this control chart
PC: STATISTICS > Control Charts > Continuous > I-MR