Home / Statistical Tools / Control Charts / Marking Outliers

Marking Outliers¶

Two ribbon commands that mark a source data cell so a control chart plots it but does not estimate its limits from it.

QXL Stat Tools > Control Charts > Outliers

Command	What it does
Define Cell(s) as Outlier(s)	marks every cell in the current selection
Remove Outlier(s) Mark	unmarks every cell in the current selection

Neither opens a dialog. Both act on whatever is selected in Excel at the moment you press them.

What the mark is¶

An Excel Note on the cell, reading Outlier. It is a note like any other you could add yourself, with one difference: Quantum XL stamps its author as QuantumXL_Outlier, and that is how the mark is told apart from a note you wrote.

You can see it on the worksheet. The cell gets the usual note indicator, and hovering shows the word Outlier.

Nothing about the cell's value changes. The number stays exactly as it was, which is the point: an outlier mark is a statement about how the analysis should treat the value, not a correction to it.

What a marked cell does to a chart¶

It is still plotted, and it no longer helps set the limits.

That distinction is the whole feature. The point stays on the chart where you can see it, so the record of what happened is intact; the centre line and the control limits are estimated as though it were not there, so one known bad reading cannot widen the limits enough to hide the next one.

The out-of-control tests still apply to it. A marked point beyond the limit is still marked as beyond the limit.

Mark a cell in a subgroup and the whole subgroup leaves the estimate. The limits are estimated from whole subgroups, so a single marked cell takes its subgroup out of the calculation rather than just itself.

What the mark is not¶

It is not a decision the software makes. Nothing in Quantum XL marks a cell as an outlier on its own; both commands act on the cells you selected, and the mark records a decision you have already made about a particular reading.

It is not a deletion. The value stays in the cell, the point stays on the chart, and the mark can be taken off again.

It does not change the out-of-control tests. A marked point is still tested and still flagged if it falls beyond a limit.

Marking cells¶

Select the cells in your source data. Any selection works: one cell, a block, several separate ranges.
QXL Stat Tools > Control Charts > Outliers > Define Cell(s) as Outlier(s).
Re-run the analysis. The marks are read when a chart is built, so an existing chart does not change until it is re-run. See Updating and Modifying Control Charts.

With nothing selected the command says Select cells in your data first. and stops.

A cell that is already marked is re-marked silently. Marking the same range twice is harmless.

The one case that is refused, and why¶

A cell that already has a note you wrote is not marked, and the command says so, listing every cell it skipped:

The following cells have existing user-created notes and were not marked as outliers:

the cell addresses

Delete those notes first if you want to mark these cells.

One cell holds one note. Marking would have to overwrite yours, so the command refuses that cell, marks the rest of the selection, and tells you which ones it left alone. Delete the note and mark the cell again if the mark is what you want.

Removing marks¶

QXL Stat Tools > Control Charts > Outliers > Remove Outlier(s) Mark over the selection.

It removes only Quantum XL's own outlier notes. A note you wrote is left exactly where it is, whatever else is in the selection, because the command matches on the author rather than on the presence of a note.

Re-run the analysis afterwards for the limits to go back to including those points.

Which analyses read the marks¶

Every control chart. The marks are scanned out of the source data range whenever an analysis is built, converted to the analysis's own coordinates, and handed to the calculation engine as the set of points to leave out of the limit estimate.

They travel with the workbook, because they are ordinary Excel notes: save, reopen, and the marks are still there.