University of California, Berkeley: Philip Stark's SticiGui: "Chapter 31: The Multinomial Distribution and the Chi-Squared Test for Goodness of Fit"
Read Chapter 31 to learn how to compare data as a percent from three or more similar groups when you are analyzing categorical data. There are several exercises and Java applets embedded in the text that are meant to further reinforce your learning. Do not skip these exercises! For instructions on how to navigate these exercises, see "Special Instructions on SticiGui Exercises and Java Applets” in the "Course Information” section above.