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Bar Graphs

A bar graph uses the height of different bars to compare quantities. [link] lists the 12 most populous countries in the world. [link] provides this same data in a bar graph. The height of the bars corresponds to the population of each country. Although you may know that China and India are the most populous countries in the world, seeing how the bars on the graph tower over the other countries helps illustrate the magnitude of the difference between the sizes of national populations.

Leading countries of the world by population, 2015 (in millions)

The bar graph shows population (millions) on the y-axis and lists various countries along the x-axis. The approximate population in 2015 for each of these countries is as follows: China = 1,369; India = 1,270; Unite States = 321, Indonesia = 255; Brazil = 204; Pakistan = 190; Bangladesh = 158; Russia = 146; Japan = 127; Mexico = 121; Philippines = 101.
The graph shows the 12 countries of the world with the largest populations. The height of the bars in the bar graph shows the size of the population for each country.
Leading 12 countries of the world by population
Country Population
China 1,369
India 1,270
United States 321
Indonesia 255
Brazil 204
Pakistan 190
Nigeria 184
Bangladesh 158
Russia 146
Japan 127
Mexico 121
Philippines 101

Bar graphs can be subdivided in a way that reveals information similar to that we can get from pie charts. [link] offers three bar graphs based on the information from [link] about the U.S. age distribution in 1970, 2000, and 2030. [link] (a) shows three bars for each year, representing the total number of persons in each age bracket for each year. [link] (b) shows just one bar for each year, but the different age groups are now shaded inside the bar. In [link] (c), still based on the same data, the vertical axis measures percentages rather than the number of persons. In this case, all three bar graphs are the same height, representing 100% of the population, with each bar divided according to the percentage of population in each age group. It is sometimes easier for a reader to run his or her eyes across several bar graphs, comparing the shaded areas, rather than trying to compare several pie graphs.

U.s. population with bar graphs

The image shows three bar graphs that represent the U.S. population. All three images reveal the same information presented in different ways. In 1970, people 19 and under made up 77.2 million or 37.6% of the population; people between ages 20 and 64 made up 107.7 million or 52.5% of the population; and people 65 or older made up 20.1 million or 9.8% of the population. In 2000, people 19 and under made up 78.4 million or 28.5% of the population; people between ages 20 and 64 made up 162.2 million or 58.9% of the population; and people 65 or older made up 34.8 million or 12.6% of the population. In 2030, the projection is that people 19 and under will make up 92.6 million or 26.4% of the population; people between ages 20 and 64 made up 188.2 million or 53.6% of the population; and people 65 or older made up 70.3 million or 20% of the population. Image (a) shows separate bar graphs for each age group in each time period (so 9 bars total). Image (b) shows the total population divided into age groups (so 3 bars total, with different color coding to identify the portions pertaining to different ages). Image (c) shows the total population divided into percentages to reveal the prediction that in 2030 (so 3 bars total, with different color coding to identify the portions pertaining to different ages).
Population data can be represented in different ways. (a) Shows three bars for each year, representing the total number of persons in each age bracket for each year. (b) Shows just one bar for each year, but the different age groups are now shaded inside the bar. (c) Sets the vertical axis as a measure of percentages rather than the number of persons. All three bar graphs are the same height and each bar is divided according to the percentage of population in each age group.

[link] and [link] show how the bars can represent countries or years, and how the vertical axis can represent a numerical or a percentage value. Bar graphs can also compare size, quantity, rates, distances, and other quantitative categories.

Comparing Line Graphs with Pie Charts and Bar Graphs

Now that you are familiar with pie graphs, bar graphs, and line graphs, how do you know which graph to use for your data? Pie graphs are often better than line graphs at showing how an overall group is divided. However, if a pie graph has too many slices, it can become difficult to interpret.

Bar graphs are especially useful when comparing quantities. For example, if you are studying the populations of different countries, as in [link] , bar graphs can show the relationships between the population sizes of multiple countries. Not only can it show these relationships, but it can also show breakdowns of different groups within the population.

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Source:  OpenStax, Principles of economics. OpenStax CNX. Sep 19, 2014 Download for free at http://legacy.cnx.org/content/col11613/1.11
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