Home / Statistical Tools / Control Charts / Xbar
Xbar¶
From Excel click...
QXL Stat Tools Tab > Control Charts > Variables > Charts in Subgroups > Xbar
This is a single panel of the Xbar-R chart
A Xbar chart is the Xbar Chart panel, the subgroup means, drawn on its own. It is not a separate analysis: the ribbon's Xbar entry opens the Xbar-R Chart dialog with the Xbar only radio already selected, and the dialog title still reads Xbar-R Chart.
Everything about the data it reads, the options it offers, and the way the limits are computed is described on Xbar-R and Xbar-S. This page covers only what is different when Xbar only is the selected variant.
Want to build one first?
The walkthroughs live with the full chart: How-To builds one step by step from sample data you copy off the page straight into Excel, and How-To with GroupBy does the same with a grouping column. Both use both panels; switch the Chart: radio group to this variant at the same point in the steps to follow along here.
What is different under Xbar only¶
- Only the upper panel is drawn. The Range panel is still computed, it is just not written to the worksheet, and it gets no row in the summary table either.
- Rules 5 through 8 stay available. They test the location panel, and the location panel is the one being drawn. The italic note that says they apply to the Xbar panel only disappears, because there is no other panel to distinguish them from.
- Reference lines are drawn. They attach to the location panel, which is present here.
- The manual limits grid still shows the Range row. Anything entered in it is accepted and computed but never becomes visible.
Getting an Xbar chart estimated with Sbar
The ribbon's Xbar entry always opens the Xbar-R dialog, so the sigma estimate offered is Rbar or the pooled standard deviation. If you want the means with an Sbar estimate instead, open Xbar-S from the ribbon and select the Xbar only radio by hand. No ribbon button produces that combination directly.
When to use it¶
- You want the subgroup means on their own, without the companion panel beside them.
- You are reading, printing or sharing one panel and the other would be noise.
If you want both panels, use Xbar-R and Xbar-S.
Output¶
The analysis writes one worksheet named Xbar Chart. Under GroupBy there is one worksheet per group, each named Xbar Chart - {GroupName}.
Worksheets are divided by GroupBy group, not by chart. Every chart belonging to a group is stacked down that one worksheet, one below the other, so selecting three measurement columns without GroupBy produces three charts on a single sheet rather than three sheets. The User Input block is written once at the top of each worksheet; everything after it repeats for each chart on the sheet.
The sheet holds the User Input block, the single Xbar Chart panel, a summary table to its right covering that panel only, and, when you entered a specification limit or a target, a capability and histogram block below it. The full layout is described on Xbar-R and Xbar-S.
When the analysis finishes, the Control Chart task pane opens on the right. See Task Pane for what it can and cannot change.