Scatter Plots
This button takes you to a screen that allows you to create scatter plots
with a number of extras:
Basic Scatter Plot
To create a scatter plot, choose the X-Variable (the
horizontal variable) and the Y-Variable (the vertical variable) from the
lists at the right, the press the "Update" button.
The scatter plot will appear in the center. Above
is the regression equation in the form
Y-Variable = Intercept + Slope *(X-Variable),
along with the RMSE = Root Mean Square Error,
and r = correlation coefficient.
(Be sure the "Blank Plot" box at the upper
left is not checked.)
Lines
Along the left, there are four boxes to choose that
will cause lines to appear on the scatter plot. The first will draw the
Regression (least
squares) line, and the second will draw the SD-Line.
The third draws two parallel lines, each one RMSE away from the regression
line, that is, it draws Regression Line
- RMSE and
Regression Line + RMSE.
The fourth draws lines two RMSE's from the regression line, at Regression
Line - 2*RMSE and Regression Line + 2*RMSE.
You can select as many or as few of these boxes as you wish.
The regressogram
In addition to the above lines, a regressogram can be drawn on the plot.
A regressogram splits the X-Variable into a number of bins, then for each
bin draws a horizontal whose height is the average of the Y-Variable
for observations in that bin. The number of bins can be set by typing
in a number in the area next to "# bins:" (This number must be between
1 and 100.)
Residuals
Checking the "Residuals" box will pop up a
window with a little scatter plot with the X-Variable as the horizontal
and the Residuals as the vertical, and a little histogram of the Residuals.
Saving the residuals
To add the residuals to the data set, just press
the "Save Residuals" button. A new variable will be created. Its
name will be Resid(i.j), where the i is the number of the
Y-Variable and j is the number of the X-Variable. Thus if the X-Variable
is first in the list of variables, and the Y-Variable is the fourth, then
the residuals will be named Resid(4.1).
The residuals saved will be for the original
variables, and not reflect any changes you might have made with adding,
deleting, or splitting.
Splitting Plots
In the little box of choices next to the "# bins"
area, one can choose whether to plot the variables using all the observations,
or whether to use just the observations with low values of the splitting
variabel, or high values of the splitting variable.In order to make use
of this option, a Splitting Variable must have already been
chosen.To do that, press the Choose
Split button.
Once the splitting variable is set, you have these choices:
-
"No Split ..." plots all the observations
-
"Split: >=" plots just the observations whose
values on the splitting variable are greater than or equal to the splitting
value
-
"Split: <" plots just the observations
whose values on the splitting variable are less than the splitting value
Press "Update" when you have made your selection.
Label/Add/Delete Points
The little choice area just to the right of the "Save
Residuals" button indicates what happens when the mouse is used to
click on the scatter plot.
-
Label Points: The name of the observation
closest to the click will appear near the click.
-
Add Points: A new observation will be added
to the scatter plot at the click.
-
Delete Points: The nearest observation to
the click will be deleted.
By hitting "Update," one can undo all the
labeling, adding, and deleting and return to the original scatter plot.
Blank Plots
To start with a blank scatter plot, select the "Blank"
option at the left, then press "Update." A plot will appear with
nothing on it. You can then add points, and delete points after you have
added them. Pressing "Update" will blank out the plot again.
Statistics
Checking the little box labeled "Statistics"
at the left will pop up the statistics (average, median, SD, minimum, maximum)
of the two variables in the existing plot, plus the residuals. If there
are added points, or deleted points, these statistics will reflect the
changes. Choosing the "Statistics" button at the top of the
screen gives the statistics for all the original variables, and does not
reflect any adding or deleting done on the plots.