Creating Probability Distribution Graphs

Creating the Basic Graph

Graphs without Shading

Choose Graph / Probability Distribution Plot / View Single
Select the appropriate distribution (binomial, normal, t, chi-square, F)
Enter the parameters for your distribution
1. Binomial: Number of trials, n and probability of success on a single trial, p
2. Normal: Mean and standard deviation. These default to mean = 0 and standard deviation = 1 for the standard normal distribution, but you can change them for non-standard normal distributions
3. t: Degrees of freedom
4. chi-square: Degrees of freedom
5. F: numerator degrees of freedom and denominator degrees of freedom
Click OK

Graphs with Shading

Choose Graph / Probability Distribution Plot / View Probability
Select the appropriate distribution (binomial, normal, t, chi-square, F)
Enter the parameters for your distribution
1. Binomial: Number of trials, n and probability of success on a single trial, p
2. Normal: Mean and standard deviation. These default to mean = 0 and standard deviation = 1 for the standard normal distribution, but you can change them for non-standard normal distributions
3. t: Degrees of freedom
4. chi-square: Degrees of freedom
5. F: numerator degrees of freedom and denominator degrees of freedom
Switch to the shaded area tab
Define the shaded area by probability and decide whether it is a right tail, left tail, or two tail probability. Then enter the area in the shaded region (usually the significance level α) into the probability box.
Click OK

Cleaning Up the Graph

You can double click any part of the graph to edit it.

Y-Scale: Double click on a number on the y-axis. You can click anywhere on the y-axis, but a number is bigger and easier to hit.
1. Under Scale Range, uncheck the Auto button for the minimum value change the minimum value to be 0. You may want to change the maximum y-value as well. For the normal distribution, I use 0.6 to flatten the curve out a little bit (the default maximum is 0.42288).
2. Click on the Show tab at the top and uncheck all the values. Alternatively, you can just delete the y-axis when you're done editing it.
3. Click OK
X-Scale: Double click on a number on the x-axis.
1. Under Scale Range, uncheck the Auto button for the minimum and maximum values and set them to be the left edge and right edge of your graph.
2. Click on the Show tab at the top and uncheck the High Axis line.
3. [Optional] Click on Font and change the font size to something a little larger. You can also change the font to Arial or some other font if you prefer.
4. You can specify the tick marks by going to Scale and choosing Position of ticks. You can either put in a space separated list (like 0 1 2 3 4 5 6 7 8 9 10) or you can use the start:stop/width notation (like 0:10/1 which means start at 0, stop at 10, count by 1's)
X-axis label: Click once on the "x" at the bottom and then press the delete key. You may also right click and choose delete.
Y-axis label: Click once on the "p" at the left and then press the delete key. You may also right click and choose delete.
Title: Double click on the title and change it.
Thicken the curve (points): Double click on the curve (points) and then change to a Custom type. Play around with the size so that it is larger and easier to see. A size of 3 is usually pretty good for the line.
Double click in the gray area outside the graph region. We would like it to be transparent.
1. Change the fill pattern to custom and set the type to none. To get to the no fill, you'll actually have to scroll up the pull down list to the box with the N in the middle.
2. Change the borders and fill lines to custom and then change the type to none

Annotating the Graph

At this point, we are ready to start adding things to the graph, rather than just changing what is there. There is a graph annotation toolbar that is active while you're editing a graph. If the toolbar does not appear on your screen, then go to Tools / Toolbars / Graph Annotation Tools and turn it on. Until this point, we have been using the Select Mode (the arrow), but now we're going into insert Text (the T) or a Lines (the line). Click on the appropriate mode to insert the right object. Here are generic instructions for each type of object.

Inserting Text

Click the T from the graph annotation toolbar
Click on the graph where you would like the upper left corner of the text to be (this can be changed later)
Type the text
Click OK
After the text is on the screen, you can edit it, change the font (to Arial), color, or size. You can also drag it to a new location on the screen since it is very unlikely that you will get it where you want it the first time
Fine control over the position of the text can be obtained by using the arrow keys or shift arrow (for medium control).

Special Text

Occasionally, you will need to create a special symbol like the Greek letter alpha, α. To do this, type the letter a and then change the font to be Symbol. The Symbol font contains the Greek letters that match up (mostly) with the Roman letters.

Inserting Lines

Click on the Line on the graph annotation toolbar
Click (and hold) the left mouse button where you would like the line to start
Drag the mouse to where you would like the line to end. You can force a horizontal, vertical, or diagonal (45 degree) line by holding the shift key down while dragging. Let up on the mouse button when you reach the destination.
If you don't get the line exactly where you want it, you can drag the line once it's on the screen. You can lengthen the lines by draging the ends, but be careful because the shift key doesn't keep it horizontal or vertical when at this point.
You can then edit the line to change the type, color, or size, or add arrows
Fine control over the position of the line can be obtained by using the arrow keys or shift arrow (for medium control)