Click Sheet 1 Tab of Customer Data.xls (or press
F4 to activate last worksheet).
Click SigmaXL > Graphical Tools > Boxplots.
Ensure that entire data table is selected. If not, check
Use Entire Data Table. Click Next.
Select Overall Satisfaction, click
Numeric Data Variable (Y) >>, select Customer Type, click
Group Category (X1) >>, check Show Mean, check
Click OK. A boxplot of Customer Satisfaction By Customer Type is produced:
The legend indicates that the solid center line is the median. The dashed red line shows the sample mean. The top of the box is the 75th percentile (Q3). The bottom of the box is the 25th percentile (Q1). The height of the box is called the Inter-Quartile Range (IQR) and is a robust measure of spread or sample variability. The data point highlighted for Customer Type 2 is a potential outlier (< Q1 – 1.5 * IQR or > Q3 + 1.5 * IQR). Note that extreme outliers are highlighted with a solid dot (< Q1 – 3 * IQR or > Q3 + 3 * IQR).
Tip: If you hover your mouse cursor in the middle of any of the Boxplot lines as shown, you will see the balloon help indicating what the line is and its numeric Y value.
Note, in Excel 2007/2010, right click on the Y-Axis and select “Format Axis".
Now we will modify the Y axis scale, showing 1 as minimum and 5 as maximum (given that the response data comes from a survey with 1-5 scale). To do this double click on the Y axis, select
Scale, modify the minimum value and maximum value
Change Category (X) axis Crosses at: to 1 as shown:
Click OK. The Boxplot axis is modified as shown below:
Click Recall SigmaXL Dialog menu or press
F3 to recall last dialog.
Overall Satisfaction, click Numeric Data Variable (Y) >>; select
Customer Type, click Group Category (X1) >>; select
Size of Customer, click Group Category (X2) >>; check
Show Mean; uncheck Show Legend:
OK. Boxplots of Customer Satisfaction By Customer Type and Size are produced:
In order to adjust the Y-axis scale for
both charts, click SigmaXL Chart Tools > Set Chart
OK. The Y-axis scale maximum and minimum are now modified for both charts.