Since you just want to do a comparison to the
variable already displayed on the control chart
and do not need control limit and centerline
calculations, it is relatively easy to add a
second analysis variable to the chart. We will
need to use the barline Statit graphics command.
Pretend as a guidance counselor I have several
students who I have given targets for their
GPA. I would like to see the quality control
chart for all of my students GPA, but also see
how their GPA compares to what I set as their
target. Follow the comments in the macro below:
Using the sample file "student.wrk",
I will create another variable
## TargetGPA to represent a line with the target
GPA values to place on top
## of my QC chart.
## Be sure this variable as the same number
of cases as the original!!
assign TargetGPA 3.2 3.4 3.5 3.6 3.7 3.3 3.4
2.5 3.0 3.2 2.8 3.2
I will first generate the I-Chart for GPA with
a /nodraw option
GPA by 2 /axis=Name /tip_stats = data x /nodraw
Next, I begin to add some custom graphics commands
## For QC charts, I need to place the barline
on chart 2
chart 2 current
Now, add the new barline using new target GPA
barline 2 TargetGPA /color=Green /linestyle=solid
/marker=zero /linewidth=5 ;
/style=line /legend="Target GPA"
Make barline 1 match format of barline 2
barline 1 /legend="GPA" /marker=zero
Use the following commands to add a nice legend
## in the upper right hand corner.
legend /box=yes /boxcolor=White ;
/boxborder=Black /location=950,900 /display
Finally, draw the chart