# TOPIC 26

# Graphical Displays of Association

Is the selling price of a house related to its size? Is a state's birth rate associated with its death rate? Is there a relationship between the fuel efficiency rating of a car and its weight? Is the life expectancy of a country's people connected in some way with how many television sets the country has? In this topic, you will begin to learn statistical techniques for addressing such questions and many more.

## Overview

Of all of the scenarios that you have studied thus far, you have yet to study relationships between two *quantitative* variables. This scenario is the subject of the final unit, which will again progress from graphical displays to numerical summaries and then proceed to mathematical models and statistical inference. In this topic, you will begin the process by investigating the concept of association and exploring the use of graphical displays called scatterplots to display the association between quantitative variables. You will also study some modifications of this basic graph, such as labeled scatterplots, and learn how to discern additional information from them.

## Preliminaries

- Do you expect that bigger houses tend to cost more than smaller houses? (Activity 26-1)
- Do you think that if one house is larger than another, then it must always cost more than the smaller house? (Activity 26-1)
- Do you expect that heavier cars tend to have better fuel efficiency (miles per gallon ratings) than smaller cars or to have worse fuel ...