University of California, Berkeley: Philip Stark's SticiGui: "Chapter 29: Testing Equality of Two Percentages"
Read Chapter 29 to learn how to compare data as a percent from two similar groups when you are analyzing categorical data. For example, suppose that you are analyzing the percent of low income women versus the percent of high income women that belong to one sample. Then, you want to compare those percentages to a different but similar sample of women. 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.