Histograms
This button allows you to create one or more histograms, with several extra
options:
Basic Single Histogram
To create a histogram for a single variable:
-
Make sure "Single" is chosen on the left-hand
side
-
Select the variable in the list at the right
-
Type in the number of bins you wish for the histogram
in the area just below "# of Bins:" (The number must be between
1 and 100.)
-
Press the "Update" button
Lines
Along the left, there are four boxes to choose that
will cause vertical lines to appear on the histogram. The first two will
draw lines at the Average
and Median, respectively.
The third draws two lines, one at Average
- SD and
one at Average + SD.
The fourth draws lines at Average - 2*SD
and one at Average
+ 2*SD. You can select as many or as few
of these boxes as you wish.
Multiple and Aligned Plots
Selecting either the "Multiple" or "Aligned"
choices at the left allows you to choose more than one variable to plot
at the same time. The steps are then
-
Choose "Multiple" or "Aligned" on the
left-hand side
-
Select the variables in the list at the right. If
you are using the program on Windows95 (and not through Netscape), you
may have to hold down the "Ctrl" key while you are selecting the
variables so that more than one can be chosen.
-
Type in the number of bins you wish. All histograms will have the same
number.
-
Press the "Update" button.
Any lines you have chosen will appear on all the histograms.
What's the difference between Multiple and Aligned?
-
Multiple: Each histogram will have bins chosen
to fit its variable
-
Aligned: All histograms will have the same
bins, so that they can be easily compared
Multiple is appropriate if the variables you
are choosing are in different units, e.g., one variable is in years and
one variable is in thousands of dollars. Aligned is often appropriate
is the variables are in the same units, e.g., one variable is the incomes
of men, and one variable is the income of women.
Split Histograms
By choosing split histograms, you will get two histograms
for the same variable. The data is split into two parts based on the Splitting
Variable. One histogram will be for the observations with low values
of the splitting variable, and the other for high values of the splitting
variable. So to use this option, one must have chosen a splitting variable.
To do that, press the Choose Split button.
Once the splitting variable is set, proceed to the steps:
-
Make sure "Split" is chosen on the left-hand
side
-
Select the variable in the list at the right
-
Type in the number of bins you wish for the histogram
in the area just below "# of Bins:"
-
Press "Update"
Label/Add/Delete Points
The little choice area just below the list of variables
indicates what happens when the mouse is used to click on a histogram 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 histogram 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 histogram.
Blank Plots
To start with a blank histogram, 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 lower right (above "# of Bins") will pop up the statistics (average,
median, SD, minimum, maximum) of the variables in the existing plot(s).
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 histograms.