Assessing Normality Example:
The following data are playing times for randomly selected songs on compact discs. Are the data normally distributed?

Times (in minutes): 2.2, 3.9, 1.9, 2.2, 4.0, 7.0, 3.9, 8.2, 2.9, 3.0, 3.6, 3.5, 3.4, 3.8, 5.3, 6.0, 3.6, 2.4, 3.9, 5.7, 2.9, 5.4, 3.8, 1.2, 4.6, 4.1, 4.7, 3.2, 2.7, 9.4.

Solution:
The over all shape of the histogram should be similar to the "bell curve" shape of the normal graph is the data is normally distributed. To draw the histogram, from the statistical data list, press "F1" (GRPH) to display the graph menu, press "F6" (SET), and then change the graph type of the graph you want to use (GPH1, GPH2, GPH3) to histogram (Hist). Then go back to graph menu, and graph it.

An additional tool for assessing normality is the normal probability plot. If the list is normally distributed, the normal probability graph will be linear. Follow the same direction as drawing histogram, except this time change the graph type, under the (SET) mode, to normal probability plot (NPP).

The histogram of the data appears to have a longer right tail, which means it is right-skewed. You can see it in the normal probability plot, which appears mostly linear, but the last few values fall to the right of the linear line. This data are not normally distributed; they are skewed to the right.