Page 311 - Statistics for Dummies

Chapter 19
Two-Way Tables and
Independence
In This Chapter
▶ Setting up two-way tables with categorical variables
▶ Delving into marginal, joint, and conditional distributions
▶ Checking for independence and dependence
▶ Having perspective on the results of two-way tables
ategorical variables place individuals into groups based on certain
Ccharacteristics, behaviors, or outcomes, such as whether you ate break-
fast 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 way around? Or
perhaps a third variable out there is related to both of them, such as prob-
lems in the home.

In this chapter, you see how to organize and analyze data from two categori-
cal variables. You find out how to use proportions to make comparisons and
look at overall patterns and how to check for independence of two categori-
cal variables. You see how to describe dependent relationships appropriately
and to evaluate results claiming to indicate cause-and-effect relationships,
making predictions, and/or projecting their results to a population.

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