Normal Probability Plot

This type of plotting is only available on the TI-83 Graphing Calculator. 
 
The normal probability graph plots each observation in the data set against the corresponding quartile 'z' of the standard normal distribution.  If the plotted points lie close to a straight line, then the graph indicates that the data are normal. 

Steps for graphing the Normal Probability Plot: 

1.  Enter the data set into list L1 by pressing  and  1: Edit. 

Data set:  15   23  25  34  17  25  35  16  19  18 34  29  14  16

2. Press   and  to set up Plot 1.  Press  to turn Plot 1 on.  Press , , , , ,  and  to select the normal probability plot. 

3. Check that the "Data List" selection has the correct list indicated.  This directs the calculator to create the normal probability plot using the desired data list. 

4. Check that the desired "Data Axis" selection highlighted - either "X" or "Y".  If the "X" Data Axis is highlighted, this directs the calculator to plot the data on the x-axis and the z-values on the y-axis.  If the "Y" Data Axis is highlighted, this directs the calculator to plot the data on the y-axis and the z-values on the x-axis. 

5. Select the desired mark to be used on the plot from the "Mark" row. 

6. Press  .  The normal probability plot should be displayed on the screen.  The normal probability plot should look like the image shown below.                 The plot on the right shows that the data point x = 14 has a y-value which is the z-value = -1.802743.  The individual z-values can be found by using the "Tracee" command on the calculator.  When using the "Trace" command, use the left and right arrows to 'jump' from one data point to another.