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A bar chart or bar graph is a chart with rectangular bars with lengths proportional to the values that they represent. The bars can be plotted vertically or horizontally. A vertical bar chart is sometimes called a column bar chart.
What it is:
A bar graph is a chart that uses either horizontal or vertical bars to show comparisons among categories. One axis of the chart shows the specific categories being compared, and the other axis represents a discrete value. Some bar graphs present bars clustered in groups of more than one (grouped bar graphs), and others show the bars divided into subparts to show cumulate effect (stacked bar graphs).
How to use it:
Determine the discrete range. Examine your data to find the bar with the largest value. This will help you determine the range of the vertical axis and the size of each increment. Then label the vertical axis. Determine the number of bars. Examine your data to find how many bars your chart will contain. These may be single, grouped, or stacked bars. Use this number to draw and label the horizontal axis. Determine the order of the bars. Bars may be arranged in any order. (A bar chart arranged from highest to lowest incidence is called a Pareto chart.) Normally, bars showing frequency will be arranged in chronological (time) sequence. Draw the bars. If you are preparing a grouped bar graph, remember to present the information in the same order in each grouping. If you are preparing a stacked bar graph, present the information in the same sequence on each bar. Bar charts provide a visual presentation of categorical data. Categorical data is a grouping of data into discrete groups, such as months of the year, age group, shoe sizes, and animals. In a column bar chart, the categories appear along the horizontal axis; the height of the bar corresponds to the value of each category.
Bar graphs can also be used for more complex comparisons of data with grouped bar charts and stacked bar charts. In a grouped bar chart, for each categorical group there are two or more bars. These bars are color-coded to represent a particular grouping. For example, a business owner with two stores might make a grouped bar chart with different colored bars to represent each store: the horizontal axis would show the months of the year and the vertical axis would show the revenue. Alternatively, a stacked bar chart could be used. The stacked bar chart stacks bars that represent different groups on top of each other. The height of the resulting bar shows the combined result of the groups. However, stacked bar charts are not suited to datasets where some groups have negative values. In such cases, grouped bar charts are preferable.
A bar chart is very useful for recording discrete data. Bar charts also look a lot like a histogram, which record continuous data. The difference is NOT that bar charts (can) have spaces between columns and histograms don't (have to have) spaces, the difference is the type of data that each represent. Discrete data is categorical data, and answers the question, "how many?". Continuous data is measurement data and answers the question, "how much?" For more on the difference, please see the excellent description from shodor.org
The first bar graph appeared in the 1786 book The Commercial and Political Atlas, by William Playfair (1759-1823). Playfair was a pioneer in the use of graphical displays and wrote extensively about them.
- Kelley, W. M.; Donnelly, R. A. (2009) The Humongous Book of Statistics Problems. New York, NY: Alpha Books ISBN 1592578659
|Wikimedia Commons has media related to Bar charts.|
- How to Construct Bad Charts and Graphs
- Directory of graph software and online tools (many can handle bar charts)
- Create A Graph. Free online graph creation tool at the website for the National Center for Education Statistics (NCES)