Making a Double Bar Graph

Your students have made and interpreted bar graphs before, but this lesson is probably their first encounter with double bar graphs. Start out by asking students what bar graphs are and where they have seen them before. Guide students to discuss the ideas that bar graphs show information with bars or rectangles, that longer or taller bars show greater numbers than short ones do, and that bar graphs may be in horizontal or vertical formats. To generate interest in the topic, help students generate and organize some data about themselves.

Materials: chart paper, chalkboard or writing board; small squares of paper or self-adhesive notes in two colors

Preparation: none

Prerequisite Skills and Concepts: Students should be familiar with bar graphs for showing data. They should know that graphs have descriptive titles and that their axes are labeled. They should be able to read from the end of a bar to its number on an axis to determine the number that is being shown.

• Say: I would like to know more about you and your interests. I'm curious about your favorite sports. Please write the name of your favorite sport on these papers—one color for the boys and another for the girls.
  Have helpers pass out the papers and collect them.

• Ask: How can we organize this data?
  Students may suggest reading the responses and sorting them into piles, then counting them.

  Make piles of the different responses, combining the boys' and girls' responses. If there are many different sports mentioned, group some of them with small numbers into an "other" pile.

• Ask: How many chose [name of sport]? How many chose [name of sport]?
  Students should count the responses in each pile.

  Make a chart of the numbers, perhaps like this one.

  Our Favorite Sports
  Soccer     Softball     Basketball     Other	9 4 6 3

• Ask: How can we make a bar graph to show this data?
  Students should suggest making axes and bars for the various sports and numbers. Engage a student or two in sketching out the bar graph.
  

• Ask: If we wanted to know how many boys and how many girls chose each sport, how can we find this information?
  Students should respond that boys' and girls' information are on paper of different colors, and they could sort and count these for each sport. Have students do so, extending the chart to show the results.

  Lead students in making a second graph beside the first one. Show students how to make two bars of different colors side by side, for boys' and girls' choices of one of the sports. Then let volunteers demonstrate how to make double bars for the other sports. Have children suggest a title for each graph. Illustrate how to show a key for the colors of the boys' and girls' bars.

  

• Say: How do the two graphs compare?
  Students should respond that the first graph shows data for the class as a whole, while the double bar graph breaks the data into two categories—for boys and for girls.

• Ask: What are some things that the double bar graph tells us?
  Students may respond with numbers of boys and girls who chose each sport. They may compare numbers—for example, more girls than boys chose soccer, and the same number of boys and girls chose softball.

• Say: We have learned to make and interpret a double bar graph. It showed our favorite sports for boys and for girls. You can make other double bar graphs to show and compare two sets of data.