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Understanding Bar Graphs and Pie Charts

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  • 0:06 Understanding Bar…
  • 0:20 Bar Graphs
  • 2:07 Reading a Bar Graph
  • 4:05 Pie Charts
  • 5:10 Reading a Pie Chart
  • 7:21 Examples and Practice Problems
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Lesson Transcript
Instructor: Chad Sorrells

Chad has taught Math for the last 9 years in Middle School. He has a M.S. in Instructional Technology and Elementary Education.

In this lesson, we will examine two of the most widely used types of graphs: bar graphs and pie charts. These two graphs can provide the reader with a comparison of the different data that is displayed.

Understanding Bar Graphs & Pie Charts

One of the more fascinating ways to record data is to put the data in a graph. Two of the more popular graphs are bar graphs and pie graphs. In this lesson, we will examine how to read and interpret the information that can be found on these graphs.

Bar Graphs

A bar graph is a graph that can be used to compare the amounts or frequency of occurrence of different types of data. Bar graphs are helpful when comparing groups of data and comparing data quickly. Let's look at the important parts of a bar graph.

All bar graphs have a graph title, which gives the reader a brief overview of the type of data that the graph contains. The graph title in this graph is 'Percentage of U.S. Population That Is Foreign-Born.'

Percentage of the U.S Population That Is Foreign-Born
Percentage of the U.S Population That Is Foreign-Born

Bar graphs also contain two axes that are labeled and also have a scale. The axis that is labeled at the bottom of the bars is referred to as the group data axis. This axis details information about the type of data that is displayed. The other axis in a bar graph is called the frequency data axis. This axis has a range of values that measures the frequency that the data occurs.

The most important part of a bar graph is the bars. These bars provide an instant comparison of data in a graph. The reader can easily compare the data to see which measure occurs the most often and if any data points have similar frequencies.

example of bar graph

Let's look at a different bar graph to sharpen our skills on labeling its parts. Looking at this new graph, there is one obvious difference. This bar graph is going horizontal instead of vertical like the first example. The title of this graph is 'Sports Shoes Sales' and is located at the top of our graph. The group data axis is located along the left side, which is directly under the bars. The title of the axis is 'Types of shoes.' The frequency data axis is located at the bottom of the graph and is labeled 'Average cost.' The bars of this graph are running horizontally.

Reading a Bar Graph

When reading a bar graph, it's important to pay attention to the intervals used on the frequency data axis. An interval is the amount of data that occurs between each section or tick mark.

Looking at the graph 'Sports Shoes Sales,' we can see that the frequency data axis is located at the bottom of the graph. Along this axis, we can see each tick mark represents $10. That is important, because there is data between each of these tick marks. Data located between two marks is often estimated to the closest value. For example, look at the bar for 'Gym Shoes.' The bar for 'Gym Shoes' ends between the $20 and $30 marks. The bar appears to be more than halfway between these two points, so a good estimate would be either $26 or $27. To read a bar graph, find the point where each bar would meet the frequency data axis.

Favorite Syndicated Programs Bar Graph
Favorite Syndicated Bar Graph

Let's look at the 'Favorite Syndicated Programs, 1999 - 2000.' This graph is also displayed horizontally, so the frequency data axis is located at the bottom of the graph.

Which program had almost nine percent of TV households viewing? The answer is Jeopardy. Looking at the Jeopardy bar, it is slightly more than nine percent, so a good estimate would be about 9.5%.

Which program had the least percentage of TV households viewing? The answer is The Jerry Springer Show. The Jerry Springer Show had the shortest bar and lies between three percent and six percent. A good estimate would be 4.5%.

Approximately what percent of TV-viewing households watched Friends? Friends had slightly more than six percent of viewers. A good estimate for this would be 6.2% of viewers.

Pie Charts

Shifting gears slightly, let's look at another popular type of graph used to display and compare data. Pie charts (also referred to as a circle graph) are circular graphs used to show the relationship of a part to a whole. A pie chart displays its data in sectors, which are parts of the circle and are proportional to the other parts displayed in the graph. Pie chart values are represented by percentages, with each chart representing 100%. Let's examine a pie chart and identify the important parts.

example of pie chart

Looking at this pie chart, the first important part is the graph title. The graph that we are looking at is titled 'What Tops Pizza.' It compares the most popular pizza toppings in relationship to one another. The title and the creative picture used for the pie chart give the reader information about the type of data displayed in the chart. Another important part of this pie chart is the sectors. These sectors are different-sized areas that divide up the circle into proportional parts. This is such a tasty graph, let's now examine how to read the information that it displays.

Reading a Pie Chart

Each sector in a pie chart is labeled with the sector title and its numerical data. In this chart, each sector is labeled with its percentage. All pie charts represent a whole amount that equals 100%. If you were to add up the percentages of each sector, it would equal 100%. For example, let's look at the pizza pie chart. The percentages listed in each sector are 13%, 14%, 19%, 43%, four percent and seven percent. By adding all of these percentages together, 13% + 14% + 19% + 43% + 4% + 7% = 100%.

The size of each sector is also proportional to its percentage. For example, the largest sector is 'Pepperoni' at 43%. Since the 'Pepperoni' sector is the largest percentage, its sector is also the largest size.

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