Data Analysis with Microsoft Excel: Updated for Office 2007

Chapter 12 Quality Control 497

If you consider teaching to be a process, with student evaluation scores as

one of its products, you can use SPC to determine whether the process is in

control. In other words, you can use SPC techniques to determine whether

the variation in scores is due to identifi able differences in the quality of

instruction that can be attributed to a particular semester’s course (that is,

special causes) or is due merely to chance (common causes).

Historical data from other sources show that s for this professor is 5.0.

Because there are fi ve observations in each subgroup, n 5 5. You can use

StatPlus to calculate the mean scores for each semester and then the average

of all 20 mean scores.

To create a control chart of the teacher’s scores:

1 Click QC Charts from the StatPlus menu and then click Xbar Chart.

2 Click the Subgroups in rows across columns option button.

3 Click the Data Values button and select the range names Score_1

through Score_5. Click OK.

4 Click the Sigma Known checkbox and type 5 in the accompanying

text box.

5 Click the Output button and send the control chart to a new chart

sheet named XBar Chart. Click OK.

Figure 12-6 shows the completed dialog box.

Figure 12-6
The Create
an XBAR
Control Chart
dialog box

6 Click OK.