Home / Statistical Tools / Control Charts / I-MR
I-MR¶
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QXL Stat Tools Tab > Control Charts > Variables > Charts as Individuals > I-MR
An I-MR chart is two stacked panels built from measurements taken one at a time. The upper panel, Individuals Chart, plots every observation as its own point. The lower panel, Moving Range Chart, plots the range of a short window of consecutive observations, a pair of neighbors by default. Read the moving range panel first: the limits on the individual values are computed from how much consecutive observations differ, so that point to point variation has to be stable before the individual values are worth judging.
The dialog is titled I-MR Chart and the worksheet it creates is also named I-MR Chart. The same dialog serves the Individuals and Moving Range ribbon entries, and it keeps the title I-MR Chart on all three. Every option in that dialog is described on the Options page.
When to use it¶
- Your measurements are continuous, and the process gives you one measurement per point in time: one reading per batch, one part per hour, one result per test run.
- There are no subgroups to form. This dialog has no Subgroups group at all, so each selected row is one plotted point and there is no subgroup size to set.
- You want both panels. If you want only one of them, the same dialog offers the Individuals and Moving Range variants, and the ribbon has separate entries for them.
If the process gives you two or more measurements per point in time, use an Xbar-R or an Xbar-S chart instead.
How it works¶
Quantum XL plots each selected row as one point on the Individuals panel, in worksheet order. The Moving Range panel plots the largest minus the smallest of the observations in a window that ends at the current point. The window length is the Moving range length: box, which is 2 by default, so each plotted moving range is normally the difference between a point and the one before it. The first point has no complete window, so the lower panel starts empty at that position.
The center line of the Individuals panel is the mean of the observations.
The limits come from a single within sigma estimated once for the whole chart (once per phase when the chart is split), using either the Average moving range, which is selected when the dialog opens, or the Median moving range. The Individuals limits sit a number of those standard deviations either side of the center line. Every point carries one observation, so nothing varies from point to point and both panels draw straight lines rather than the stepped limits of a subgrouped chart.
The Moving Range panel uses the same estimate. Its center line is the moving range expected from a window of that length, and its limits are fixed multiples of it. The lower limit is held at zero, so at the default moving range length and the default sigma multiplier the panel can only signal upward.
Two settings change what the limits describe rather than how they are computed. Estimate Limits From computes the limits from the first few points only and extends them across the whole chart. Split Control Limits divides the chart into phases, each with its own center line and limits.
The exact formulas are on the Math Details page.
Output¶
The analysis writes one worksheet per chart, named I-MR Chart. On it, from the top:
- A User Input block in the first two columns, holding the analysis title, the columns you selected, and whether the calculation type was Excel or GroupBy. Modify Existing Analysis reads it back.
- The Individuals Chart panel, plotting each observation with its center line and control limits, plus the zone lines, reference lines, and phase dividers if you asked for them. Points that broke an enabled out-of-control test are drawn in a different color.
- The Moving Range Chart panel below it, aligned so its points line up vertically with the panel above.
- A summary table to the right, listing for each panel the center line, the control limits where they exist, the count of out-of-control points, and the count of points you marked as outliers. A transformation adds rows naming the type and its parameters; a split chart adds a per-phase breakdown.
- A capability and histogram block below the panels, but only when you entered a specification limit or a target on the Capability tab.
When the analysis finishes, the Control Chart task pane opens on the right. See Create Control Charts for what it can and cannot change.