Investigating Income Inequality in the U.S.
Lesson Overviews, Learning Objectives, & Sample Lessons

Lesson 1. What is income inequality?

The activities in this opening lesson are designed to engage students in the topic of income inequality and to introduce them to the Data Investigation Cycle.

Learning Objectives

Students will be able to

• Explain in general terms how income from wages is distributed among wage earners in the U.S.

• Pose questions about income inequality and identify which ones can be answered with data

• Identify the four steps of the Data Investigation Cycle

Lesson 2. How do we learn about people’s incomes in the U.S.?

The activities in this lesson introduce students to the primary data source of the module: The U.S. Census Bureau’s American Community Survey. Students will discuss strengths and weaknesses of the data and connect tables and graphs of data from the survey, displayed using CODAP.

Learning Objectives

Students will be able to:

• Describe how the variables in a data set relate to items in the ACS questionnaire

• Describe and distinguish between between the types of income recorded by the ACS

• Describe how data in a data table relate to data in a graph

Lesson 3. What was the average income in the U.S. in 2017, and how accurately can we estimate it?

Students will use sample data from the ACS to estimate the mean income of the U.S. population in 2017. CODAP will calculate the mean for different samples, and students will consider how increasing the sample size reduces the sample-to-sample variation. A goal is to convince students that a sample of just 1,000 cases provides a reasonable estimate of the mean of the entire population.

Learning Objectives

Students will be able to:

• Graph and describe what the distribution of incomes looked like in the U.S. in 2017

• Estimate the average annual income from wages for individuals in the U.S. in 2017

• Explain what sample size can provide a reasonable estimate of the average annual income from wages in the population

SAMPLE LESSON: Lesson 4. How have middle-income earners in the U.S. been doing over time?

Students will make some predictions about how average income and the distribution of income has changed in the last 50+ years. Then they will use CODAP to examine the U.S. income distribution at three points in time, exploring the differences between two measures of center: mean and median. Students will examine how the two measures of center change relative to each other based on the skewness of the distribution.

Learning Objectives

Students will be able to:

• Describe the difference between the mean and the median of a distribution

• Distinguish between typical income and average income

• Explain how the shape of a distribution influences the location of the mean and median in relation to one another

• Explain why the median is less influenced by extreme values than the mean

• Describe how mean and median incomes in the U.S. have changed over time, and provide implications for this pattern

Teacher Materials

➤ Teacher Guide

➤ Slides

➤ Activity: Mean and Median Cards

➤ Teacher Resource: Census, ACS Questions and Answers

➤ Teacher Resource: Current v Constant Dollars Info from Census Bureau

Student Materials

➤ Student Document

➤ Google Form

Lesson 5. How have higher- and lower-income earners in the U.S. been doing over time?

Students will investigate the incomes of individuals at different percentiles of the U.S. income distribution. By examining these comparison points, students will develop the practice of examining the features of an entire distribution. Students will then examine how U.S. incomes at different percentiles have changed over time. This lesson prompts students to think about how they might measure income inequality in the U.S. and to assess its scale using different tools (such as the mean, median, and percentiles of the income distribution).

Learning Objectives

Students will be able to:

• Identify the incomes at different percentiles of the income distribution

• Describe how higher- and lower-income earners have been doing over time

• Quantify the variability within the U.S. income distribution using the interquartile range (IQR)

• Describe how measures of center, variability, and shape in the U.S. income distribution have changed over time, and what these changes suggest about income inequality in past decades and today

Lesson 6. How much income inequality exists between males and females in the U.S.?

This lesson focuses on the theme of income inequality between groups and asks students to investigate: Is there income inequality between males and females in the U.S.? To explore this question, students will examine the incomes of males and females in a sample of the U.S. population from 2017 to see whether/how they differ. They will also speculate about what may explain a gap in incomes by sex.

Learning Objectives

Students will be able to:

• Compare the mean and median incomes for a sample of males and females in the U.S.

• Compare the variability in incomes for a sample of males and females in the U.S.

• Estimate the difference in typical incomes between males and females

• Summarize a conclusion in response to a question, supported with clear and accurate evidence, including graphical displays

Lesson 7. Does education explain the wage gap between males and females?

This lesson continues to explore income inequality among males and females. Lesson 6 revealed that typical (median) incomes for males are higher than for females in the U.S. What could help explain this gap? Could differences in education levels between males and females play a role?

The key idea of this lesson is to consider whether introducing a third variable into the analysis can explain or even change the original association between two variables. Specifically, students explore whether education level may be a confounding variable and how it may affect the male-female wage gap.

Learning Objectives

Students will be able to:

• Describe how a third confounding variable may affect the association between two variables

• Analyze the association of two variables across different categories of a third variable

SAMPLE LESSON: Lesson 8. Final Data Investigations

The module wraps up with a final data investigation in which students will examine whether the male-female wage gap changes after including a third variable other than education level in the analysis. Students will conduct all four steps of the Data Investigation Cycle to complete this investigation. Many teachers opt to have students work in pairs or groups of three to complete this investigation, though it is also possible to have students complete this individually. Example questions that students may choose to explore:

• Could the wage disparity between males and females be related to the number of hours or weeks that they work? (i.e. Are females more likely to be part- time workers?)

• What does the wage gap between males and females look like among people of a particular racial/ethnic background?

• What does the wage gap between males and females look like among people in different geographic regions or divisions of the U.S.?

• What does the wage gap between males and females look like among people in a particular age group?

• What does the wage gap between males and females look like among people based on whether or not they have been married?

• What does the wage gap between males and females look like among people based on whether or not they have children?

Teacher Materials

➤ Teacher Guide

➤ Slides

➤ Teacher Resource: Creating and Recoding Variables in CODAP

Student Materials

➤ Income Inequality Final Data Investigation Assignment

The full set of materials are freely available for use, but we ask you to provide us with some information about your context by completing this form.

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