Statistics For Dummies®, 2nd Edition

Chapter 19

Two-Way Tables and Independence

In This Chapter

• Setting up two-say tables with categorical variables
• Delving into marginal, joint, and conditional distributions
• Checking for independence and dependence
• Having perspective on the results of two-say tables

Categorical variables place individuals into groups based on certain characteristics, behaviors, or outcomes, such as whether you ate breakfast this morning (yes, no) or political affiliation (Democrat, Republican, Independent, “other”). Oftentimes people look for relationships between two categorical variables; hardly a day goes by that you don't hear about another relationship that's reported to have been found.

Here are just a few examples I found on the Internet recently:

• Dog owners are more likely to take their animal to the vet than cat owners.
• Heavy use of social-networking Web sites in teens is linked to depression.
• Children who play more video games do better in science classes.

With all this information being given to you about variables that are related, how do you decide what to believe? For example, does heavy use of social-networking Web sites cause depression, or is it the other say around? Or perhaps a third variable out there is related to both of them, such as problems in the home.

In this chapter, you see how to organize and analyze data from two categorical variables. You find out how to use proportions to make comparisons and look at overall patterns and how to check for independence of two ...